Moroccan boxer Hassan Saada has been arrested on suspicion of attempting to rape two maids working at the Olympic Village.
Saada, a light-heavyweight boxer who was due to begin his campaign in Rio over the weekend, was detained just hours before the Olympic opening ceremony following the alleged incident which occurred two days ago.
A statement from the Rio civil police said: "The civil police of the 42nd police station ... arrested on the morning of Friday, August 5, the boxing Moroccan athlete, Hassan Saada.
"According to the investigation, on the third of this month, the athlete would have raped two Brazilian maids who worked in the athletes' village. The arrest took place in the Olympic Village."
Saada had been drawn to face Turkey's Mehmet Nadir Unal in the opening round, with the bout scheduled for Saturday at around 12.30pm, but the 22-year-old's arrest casts extreme doubt on the fight going ahead.
He earned his place in the Games at the 2016 AIBA World Olympic Qualifying Tournament, and had he beaten Unal, he would have faced Julio Cesar La Cruz, ranked third in the AIBA 81kg category.
The arrest is the latest setback following a fraught build-up to the Olympics, which has been dominated by Russian doping, the Zika virus and issues of security.
The International Olympic Committee said in a statement: "We are aware that an athlete has been taken into police custody today. Rio 2016 is following-up to assist with the investigation and keeping us informed."
A Rio 2016 spokesman added: "We are aware of the case, a complaint was made and police detained an athlete in the village. We are following and collaborating with the investigation."
Press Association Sport attempted to contact a Moroccan Olympic official but there has been no immediate reply.