The NFL dismissed Myles Garrett's appeal against suspension on Thursday as a league spokesman said investigators found no evidence Pittsburgh Steelers quarterback Mason Rudolph uttered a racial slur at the Cleveland Browns defender before last week's mass brawl.
Garrett was banned for at least the rest of the season last Friday, a day after ripping off Rudolph's helmet and smashing it down on the Steelers player's uncovered head near the end of the Browns 21-7 win.
The 23-year-old defensive end's ban is the longest suspension ever handed down for a single on-field incident.
Garrett appeared at an appeal hearing in New York on Wednesday in a bid to reduce the length of his suspension.
However the NFL said Thursday appeals officer James Thrash had "upheld all discipline issued to Myles Garrett."
A league spokesman later said NFL officials had found no evidence Rudolph used a racial slur against Garrett before the fight erupted.
The Steelers and lawyers for Rudolph had angrily lashed out at Garrett over the allegation in statements issued earlier Thursday, describing them as "shameful."
"Mason vehemently denies the report of being accused of using a racial slur during the incident Thursday night in Cleveland," the Steelers said in a statement.
"He will not discuss this accusation any further and his focus remains on preparation for Sunday's game against the Cincinnati Bengals."
Rudolph's attorney Timothy Younger said the allegation of racism by Garrett was a "desperate attempt to mitigate his suspension" and questioned why the Cleveland player had not raised it before his appeal.
"This is a lie," Younger said in a statement. "This false allegation was never asserted by Garrett in the aftermath of the game, never suggested prior to the hearing, and conspicuously absent in the apology published by the Browns and adopted by Garrett.
"The malicious use of this wild and unfounded allegation is an assault on Mason's integrity which is far worse than the physical assault witnessed on Thursday. This is reckless and shameful. We will have no further comment."
In a statement on Twitter issued late Thursday, Garrett appeared to stand by the claim of a racial slur, complaining he had made the allegation in what he had believed was a private appeals hearing.
- Lack of restraint -
"I was assured that the hearing was space that afforded the opportunity to speak openly and honestly about the incident that led to my suspension," Garrett wrote.
"This was not meant for public dissemination, nor was it a convenient attempt to justify my actions or restore my image in the eyes of those I disappointed.
"I know what I heard. Whether my opponent's comment was born out of frustration or ignorance, I cannot say. But his actions do not excuse my lack of restraint in the moment, and I truly regret the impact this has had on the league, the Browns and our devoted fans."
The league meanwhile said that Rudolph's Steeler teammate Maurkice Pouncey's three-game suspension would be reduced to two games.
Pouncey, who rushed to Rudolph's defence, will miss the Steelers' Week 13 rematch with the Browns and this Sunday's game at Cincinnati.
Browns defensive tackle Larry Ogunjobi's one-game suspension was upheld after he came into the brawl late and hit an unsuspecting Rudolph from behind knocking him to the ground.
Myles Garrett hits Mason Rudolph with the Pittsburgh quarterback's helmet during a brawl last week