Plaintiff Willie Horne appeals from an order of the United States District Court for the Northern District of New York dismissing his action brought under 42 U.S.C. § 1983. The only substantial issue on appeal concerns Horne’s claim that, while a prisoner in New York state custody, he was denied due process when defendants, various prison system officials, failed to provide him with “counsel substitute” in a disciplinary hearing that resulted in his confinement in the prison’s Special Housing Unit (“SHU”) for six months. The district court dismissed plaintiffs claim under the authority of Sandin v. Conner, 515 U.S. 472, 115 S.Ct. 2293, 132 L.Ed.2d 418 (1995), concluding that Horne had not suffered the kind of “atypical and significant hardship” as a result of the disciplinary proceedings that might implicate the Due Process Clause. We need not reach the Sandin issue. All the time Horne served in the SHU was pursuant to a disciplinary sentence that did not violate any clearly established procedural right. Defendants accordingly are entitled to qualified immunity. We affirm the dismissal of Horne’s claim.
BACKGROUND
In April 1984, Horne entered state prison and began serving a 9-18 year sentence for second degree attempted murder. He was subsequently placed in the Eastern New York Correctional Facility (“Eastern”), where the events at issue in this appeal took place. It is not disputed that, as the court below stated, Horne “is functionally illiterate and has an intelligence level that is so low that he can be classified as mentally retarded.”
After arriving at Eastern, Horne was enrolled in remedial education classes. On December 13, 1984, a female civilian volunteer teacher at the prison submitted a disciplinary report stating that Horne had violated prison rules by encouraging her to engage in sexual acts with him. She reported that Horne said to her, “Just give me a little kiss on the cheek or anywhere else you please.” He said he “loved older women and needed somebody like me.” He added, “I wouldn’t do bad to a woman and she gives it up cause she wants *28it.” The teacher reported Horne “didn’t want to leave [the] room” [where the two were alone] and followed her to her next class. She said she felt “an imminent danger of being accosted.”
In response to the complaint, on December 19,1984, defendant Arthur Kracke, an official at Eastern, held a disciplinary hearing. An employee assistant of the facility met with Horne in advance to help him prepare for the hearing, but was not present with Horne when the hearing was conducted. Kracke found plaintiff guilty of the charges, sentenced him to one year in the SHU, and recommended that plaintiff lose one year of “good time” credits. Plaintiff appealed this sentence to defendant Donald Selsky, the Director of Special Housing and Inmate Discipline, who, in January 1985, modified the sentence to eight months in the SHU and eight months recommended loss of good time credits.
In April 1985, Horne brought an Article 78 action in New York state court, seeking to have the results of the disciplinary hearing declared void and expunged from his record. In May 1985, while the Article 78 action was pending, Selsky reversed the results of the prior disciplinary hearing — noting that he did so “after discussion with [the] Attorney General’s Office” — and directed that an “[assistant should be present at [the] re-hearing.”
Pursuant to this directive, defendant Joseph Demskie, an official at Eastern, conducted a new hearing on the disciplinary charges on May 9, 1985. At this second hearing, Horne was provided with an employee assistant under the then-current version of the governing regulation. The duties imposed by the regulation on the employee assistant were primarily to advise and render requested assistance; they did not include taking the initiative in mounting a defense. See 7 N.Y.C.R.R. § 251-4.2 (1983) Horne’s employee assistant acting under these regulations did not take initiative in presenting any defense on Horne’s behalf.
Demskie found Horne guilty of the misbehavior charges, sentenced him to 300 days in the SHU, and recommended loss of 300 days of good time credits. On May 28, 1995, Selsky again modified Horne’s sentence, to six months in the SHU and six months recommended loss of good time credits. Horne was released from the SHU and returned to general prison population thirteen days later, as his time spent in the SHU had reached the six months to which he was now sentenced.
In November 1985, the New York Attorney General’s office withdrew its opposition to Horne’s still-pending Article 78 proceeding. As a result, by Order of the New York Supreme Court dated December 19, 1985, (Traficanti, /.), the hearing determinations of December 19, 1984 and May 9, 1985 were “annulled and vacated,” the charges were dismissed with prejudice, Horne’s good time credits were restored, and the references to the disciplinary actions were expunged from his records.
In June 1986, Horne brought this suit. Horne contends, inter alia, that defendants violated his due process rights by failing to provide “counsel substitute” at the disciplinary hearings. The gist of the claim is that the duties prescribed for the employee assistant under the New York regulations do not go far enough because they require only passive assistance in the nature of explanations and responses to requests for help and do not require such proactive assertion of a defense as might be rendered by a “counsel substitute.” Horne’s complaint was later amended to add, inter alia, an Eighth Amendment claim based on the theory that defendants violated Horne’s right to be free from cruel and unusual punishment “by severely punishing him for acts for which he was not culpable due to mental retardation” and “by their infliction of punishment which was grossly disproportionate to the infraction alleged to have occurred and shocking to the conscience.”
A bench trial was held before Magistrate Judge Smith in April 1995.1 At the close of the evidence, each side moved for judgment *29as a matter of law pursuant to Fed.R.Civ.P. 50. Before the court rendered a decision, the Supreme Court decided Sandin. The magistrate judge solicited additional evidence and briefing on Sandin’s application to Horne’s case. In addition, Horne moved to amend the complaint to add causes of action based on the Equal Protection Clause, the Americans with Disabilities Act, and the Rehabilitation Act.
In a Memorandum Decision and Order dated December 3, 1996, Magistrate Judge Smith set forth his findings of fact and conclusions of law pursuant to Fed.R.Civ.P. 52(a). The magistrate judge first found that Horne had either abandoned or failed to prove each of his claims other than the due process claim. In addition, the magistrate judge denied plaintiffs post-trial motion to amend his complaint. With respect to the due process claim, the magistrate judge concluded that Horne’s confinement in the SHU “although certainly less pleasant than confinement in [the] general population,” did not constitute, under Sandin, the kind of “atypical and significant hardship” in the avoidance of which a state might conceivably create a liberty interest. “Accordingly, plaintiffs sole remaining claim in this action (i.e., that as a functionally illiterate and mentally retarded prisoner he was entitled to ‘counsel substitute’ at his disciplinary hearings) is without merit, as plaintiffs disciplinary hearings were, under the facts and circumstances of this case, not subject to the protections of the Due Process Clause.”
The magistrate judge ordered Horne’s complaint dismissed and judgment entered in favor of defendants. See Horne v. Coughlin, 949 F.Supp. 112 (N.D.N.Y.1996). This appeal followed.
We affirm, but for a different reason. Horne’s time served in the SHU was pursuant to a proceeding that did not violate any clearly established right. The defendants were accordingly entitled to qualified immunity under Harlow v. Fitzgerald, 457 U.S. 800, 102 S.Ct. 2727, 73 L.Ed.2d 396 (1982).
DISCUSSION
I. Due Process Claim
“Qualified immunity protects prison officials from personal liability [for damages] under § 1983 when their ‘conduct does not violate clearly established statutory or constitutional rights of which a reasonable person would have known.’ ” Walker v. McClellan, 126 F.3d 127, 129 (2d Cir.1997)(quoting Har low, 457 U.S. at 818, 102 S.Ct. at 2738).2 “In determining whether a right was clearly established at the time defendants acted, we examine whether the right was defined with reasonable specificity; whether the decisional law of the Supreme Court and the applicable circuit court supports its existence; and whether, under preexisting law, a defendant official would have reasonably understood that his acts were unlawful.” Rodriguez v. Phillips, 66 F.3d 470, 476 (2d Cir.1995).
Horne claims that the duties imposed by regulation on the employee assistant assigned to aid him at the second hearing did not satisfy due process requirements. According to the regulation,
The assistant’s role is to speak with the inmate charged, to explain the charges to the inmate, interview witnesses and to report the results of his efforts to the inmate. He may assist the inmate in obtaining documentary evidence or written statements which may be necessary. The assistant may be required by the hearing officer to be present at the disciplinary or superintendent’s hearing.
7 N.Y.C.R.R. § 251-4.2 (1983). Horne contends that due process requires more—that an inmate in Horne’s position be furnished with “counsel substitute,” which we understand to mean an assistant who, although not a lawyer, would approach the hearing as a lawyer would, viewing his obligations as going beyond the inmate’s instructions to include taking the initiative to protect the inmate’s rights and present a defense.
*30We find no clearly established law, in 1985 or now, requiring more than the regulation called for. Plaintiff relies principally upon Wolff v. McDonnell, 418 U.S. 539, 94 S.Ct. 2963, 41 L.Ed.2d 935 (1974), in which the Supreme Court discussed the procedural requisites of prison disciplinary hearings. Wolff held, for example, that prisoners are entitled to advance written notice of the charges against them, a written statement by the prison factfinders as to the evidence relied upon by them, and the opportunity to call witnesses and present documentary evidence “when permitting [them] to do so will not be unduly hazardous to institutional safety or correctional goals,” but that prisoners are not necessarily entitled to retained or appointed counsel. Id. at 563-70, 94 S.Ct. at 2978-81.
Plaintiff contends his right to “counsel substitute” was established by the following passage in the Wolff opinion:
Where an illiterate inmate is involved, ... or where the complexity of the issue makes it unlikely that the inmate will be able to collect and present the evidence necessary for an adequate comprehension of the case, he should be free to seek the aid of a fellow inmate, or if that is forbidden, to have adequate substitute aid in the form of help from the staff or from a sufficiently competent inmate designated by the staff.
Id. at 570, 94 S.Ct. at 2982.
We do not think this language clearly establishes Horne’s right to counsel substitute. As a preliminary matter, the passage was dictum. As the Court acknowledged, there was no indication that the prisoner McDonnell qualified for any such assistance. See id. More importantly, the passage is ambiguous. Plaintiff urges that Wolff’s expressed concern for inmates unable “to present” evidence implies that an assistant must be prepared to go beyond the inmate’s instructions in “presenting” the inmate’s case. This is at best one possible reading of the Wolff dictum. It is far from clear that the Supreme Court intended in that advisory passage to lay down the rule plaintiff here advocates. The sentence from Wolff does not specify that the assistant- should be instructed to take initiative, rather than simply respond to the inmate’s requests for assistance. The Wolff opinion made clear furthermore that it was leaving the contours of the assistant’s role to be developed in future cases. See id. (“We need not pursue the matter further here ... for there is no claim that the named respondent ... is within the class of inmates entitled to advice or help from others in the course of a prison disciplinary hearing.”). Finally, any claim that Wolff established a right to counsel-like assistance is in some tension with Wolff’s explanation, in denying prisoners a right to actual counsel, that “insertion of counsel into the disciplinary process would inevitably give the proceedings a more adversary cast and tend to reduce their utility as a means to further correctional goals.” Id. at 570, 94 S.Ct. at 2981. This rationale may well apply also to the “insertion” of counsel substitute.
Plaintiff further relies upon Vitek v. Jones, 445 U.S. 480, 100 S.Ct. 1254, 63 L.Ed.2d 552 (1980) and Hewitt v. Helms, 459 U.S. 460, 103 S.Ct. 864, 74 L.Ed.2d 675 (1983). Hewitt merely stated, in dicta, that “Wolff required ... the aid of a staff member or inmate in presenting a defense, provided the inmate is illiterate or the issues complex.” 459 U.S. at 465 n. 3, 103 S.Ct. at 868 n. 3. In Vitek, a plurality of the Court stated that “prisoners who are illiterate and uneducated have a greater need for assistance in exercising their rights” and that counsel is required for inmates “thought to be suffering from a mental disease or defect requiring involuntary treatment” because “such ... prisoners are] more likely to be unable to understand or exercise [their] rights.” 445 U.S. at 496-97, 100 S.Ct. at 1265-66. These statements, taken together with Wolff, do not establish with clarity that Horne had a right at his disciplinary hearing to counsel substitute.
Plaintiff finally relies upon this court’s opinion in Ron v. Wilkinson, 565 F.2d 1254 (2d Cir.1977). In Ron, we reversed the district court’s dismissal of an inmate’s habeas claim. The inmate claimed that he had a right, under the Constitution and prison regulations, to representation at a hearing that resulted in loss of good time. The district court dismissed the inmate’s claim without a hearing on the ground, among others, that *31the inmate suffered no prejudice from the lack of representation. We held that the district court should have held a hearing on the plaintiffs entitlement to representation. 565 F.2& at 1256-58. We further noted that plaintiffs “claim to the right of some type of representation at the ... hearing was a serious one” under Wolff and that it was “by no means apparent that substitute representation would have been fruitless.” Id. at 1256, 1257. We did seem to assume that Wolff might require “substitute counsel or ... a ‘forceful’ representative” whose tasks would include arguing and objecting. Id. at 1257. But this discussion was speculative and it did not “clearly establish[ ]” the right to counsel substitute conforming to the model plaintiff advocates. Harlow, 457 U.S. at 818, 102 S.Ct. at 2738.
Thus, plaintiffs claimed “right” to counsel substitute rests only on inconclusive dicta. The authorities cited by plaintiff do not compel the conclusion that the Due Process Clause required that Horne be furnished with an assistant who would act in the manner of counsel, seeking on his own initiative to develop a defense strategy, examine witnesses, or argue on Horne’s behalf. Finally, we note that subsequent to Horne’s second hearing, this Court stated that “an inmate’s right to assistance is limited_ [A]n assistant must be assigned to the inmate to act as his surrogate—to do what the inmate would have done were he able. The assistant is not obliged to go beyond the specific instructions of the inmate because if he did so he would then be acting as counsel in a prison disciplinary proceeding, assistance to which a prisoner is not entitled.” Silva v. Casey, 992 F.2d 20, 22 (2d Cir.1993)(per curiam); see Purnell v. Lord, 952 F.2d 679, 684 (2d Cir.1992).
We need not discuss Horne’s contention that his rights were violated at the first hearing, because it became a nullity. All findings and penalties imposed at the first hearing were vacated,3 and all the penalties Horne suffered were imposed at the second hearing.4 See Harper v. Lee, 938 F.2d 104, 105-06 (8th Cir.1991)(per curiam).
We therefore affirm the dismissal of Horne’s due process claim because defendants were protected by qualified immunity.
II. Remaining Claims
Horne also asserts that his six-month SHU confinement constituted cruel and unusual punishment under the Eighth Amendment because it was imposed without regard to his diminished mental capacities and was grossly disproportionate to the offense. “Restraints on an inmate do not violate the amendment unless they are ‘totally without penological justification,’ ‘grossly disproportionate,’ or ‘involve the unnecessary and wanton infliction of pain.’” Smith v. Coughlin, 748 F.2d 783, 787 (2d Cir.1984) (quoting Rhodes v. Chapman, 452 U.S. 337, 346, 101 S.Ct. 2392, 2399, 69 L.Ed.2d 59 (1981)). We do not think Horne’s six-month SHU detention for making sexually threatening comments to a civilian volunteer violated these standards.
Finally, plaintiff argues that the magistrate judge erred in denying his post-trial motion to amend his complaint to add claims under the Equal Protection Clause, Section 504 of the Rehabilitation Act, 29 U.S.C. § 794, and the Americans with Disabilities Act, 42 U.S.C. § 12101 et seq. “As a general matter, the district court has discretion whether or not to grant leave to amend, and its decision is not subject to review on appeal except for an abuse of discretion.” Hillburn v. Maher, 795 F.2d 252, 264 (2d *32Cir.1986)(internal quotation marks and citations omitted), cert. denied, 479 U.S. 1046, 107 S.Ct. 910, 93 L.Ed.2d 859 (1987). In the circumstances presented here, the magistrate judge was well within his discretion in denying the amendments.
CONCLUSION
The judgment of the district court is affirmed.
. By order dated June 14, 1994, the case had been referred to Magistrate Judge Smith by Judge McCurn for all proceedings and entry of final judgment with the parties' consent. See Fed.R.Civ.P. 73.
. In a letter submitted after argument, counsel for plaintiff asks us to consider his claim for injunctive relief. We decline to do so. Although Home’s complaint sought injunctive relief, he failed to litigate the issue of his entitlement to such relief in the court below or on appeal. We conclude that the claim is not before us.
. Horne is not entitled to relief in connection with the recommended loss of good time credits, since Horne's credits were ultimately restored without any loss and his disciplinary record expunged.
. It should be clear from the discussion in the dissenting opinion that Horne did not spend five months of administrative confinement waiting for his second hearing. The 5-month period he spent in SHU pursuant to his first disciplinary sentence (before it was voided), and the few days spent thereafter awaiting the second hearing, were all credited to the service of his eventual six-month sentence. As a result his six months were completed and he was released from SHU thirteen days after the six-month sentence was imposed on May 28, 1995. Thus the six months to which Horne was ultimately sentenced was the only time he spent in the SHU.