The allegations have not been proved, and the existence of the investigations does not imply that McGregor is guilty of any crime.

“Conor McGregor is frequently the subject of rumors,” a publicist for the fighter said in an emailed statement. “He emphatically denies any report accusing him of sexual assault.”

A lawyer for McGregor in Dublin did not respond to messages seeking comment.

Born in a tough, working-class section of Dublin, McGregor has helped propel U.F.C.’s popularity worldwide, though he has been involved in a flurry of police cases throughout his career.

Flanked by two bodyguards, McGregor appeared in court last week to answer charges of assaulting an elderly man at a pub in April. That case is still pending, with another hearing scheduled for next month. Security footage purporting to show the incident was leaked to the celebrity news website TMZ.

McGregor has participated in only one U.F.C. fight since 2016, a defeat last October to Khabib Nurmagomedov that ended in disgrace when a brawl broke out between their rival camps at the end of the fight. McGregor announced his retirement from the sport in March, only to hint several times that he would get back into the ring. The UF.C., which did not respond to a request for comment from The New York Times, has not announced any upcoming bouts featuring McGregor.