South Korea has filed a protest over defending champion Park Tae-hwan's disqualification in the 400-metre freestyle event on the opening day of the Olympic swimming competition.
Park was disqualified by a judge on the pool deck for a false start, Swimming governing body FINA said.
The FINA Bureau will hold a jury of appeal to decide the case.
Park was first to touch the wall on Saturday and appeared bewildered when told of the disqualification, saying he needed to ask his coach what happened.
Sun Yang of China led the heats, while Ryan Cochrane of Canada took the last qualifying position in eighth. Cochrane could miss out on the final later Saturday if Park is reinstated.