A Nevada man claims Mayweather directed his bodyguards to attack him at a Las Vegas casino last year, according to a lawsuit filed in a state court in Las Vegas last Friday.
The man says he tried to take a photograph of the undefeated boxer and asked about a fight with another star boxer.
It is alleged that Mayweather's bodyguards attacked Anthony Cliff near a valet parking stand at the Palms Casino Resort on March 27, 2010, after Mayweather accused Cliff of "disrespecting" him.
Mayweather's bodyguards allegedly struck Cliff in the face, slamming his head into the ground. They then kicked him repeatedly in his back and side, the lawsuit says.
Mayweather's attorney and a spokesman for the Palms have not responded to requests for comment.
The suit accuses Mayweather of assault and battery, intentional infliction of emotional distress and negligent hiring, training, supervision and retention of employees.
Cliff claims he first spotted the boxer inside the casino and tried to take his photo. He was told by a bodyguard that he could not do so.
The lawsuit alleges Cliff walked away, but later ran into Mayweather again at the valet stand. Cliff then asked someone in Mayweather's entourage about a possible match between Mayweather and another boxer.
The question seemed to infuriate Mayweather and his group, who surrounded Cliff and began threatening him, according to the lawsuit.
Mayweather told Cliff he was disrespectful and allegedly give his bodyguards a "thumbs down" gesture, "which was a sign for the bodyguards to attack," the lawsuit claims.
The lawsuit does not clarify which Mayweather rival Cliff was asking about.
The Palms was also named in the 43-page lawsuit for allegedly failing to provide adequate security. Cliff claims the casino's valet and security staff did nothing to help him during or after the alleged beating.
Cliff claims he feared for his life after the assault.
Mayweather is scheduled to fight Victor Ortiz on September 17. Negotiations to pit Mayweather against Manny Pacquiao have stalled.
Mayweather has a history of court dealings. He failed to turn up for a court-ordered deposition in Las Vegas earlier this month in a federal lawsuit alleging he defamed Pacquiao.
Mayweather and Pacquiao are considered among the best fighters in the world, though they've never met in the ring, partly because Mayweather's camp questioned Pacquiao's refusal to submit to drug testing.
Mayweather also faces felony charges stemming from a domestic argument and misdemeanour harassment and battery charges in separate cases.
He is undefeated in 41 fights, having won titles in five divisions.