Conor McGregor has been arrested on suspicion of attempted sexual assault and indecent exposure in Corsica, according to French media reports.
A spokesman for the retired mixed martial arts star told the AFP news agency that the Irishman "vigorously denies any accusation of bad behaviour".
The 32-year-old former featherweight and lightweight champion was taken into custody on Thursday and released on Saturday, the French news site 20 Minutes reported.
Emmanuelle Ramon, McGregor's lawyer, has said his client was "released before the legal end of police custody and without any judicial review".
In a statement sent to AFP, the prosecutor's office said: "Following a complaint filed on 10 September denouncing acts that could be described as attempted sexual assault and sexual exhibition, Mr Conor Anthony Mac Gregor (sic) was the subject of a hearing by the gendarmerie services."
The statement gave no details of the former fighter's alleged offences.