The 24-year-old U.S. star, considered to be the greatest gymnast of all time, huddled with a trainer after landing her vault. She then exited the competition floor with the team doctor.
Biles returned several minutes later. She took off her bar grips, hugged teammates Grace McCallum, Sunisa Lee and Jordan Chiles before putting on a jacket and sweatpants.
The Americans will be forced to finish the rest of the competition without her, severely hampering their bid to claim a third straight Olympic title.
The U.S. began finals on vault, with Biles going last. She was supposed to do an “Amanar,” a vault that begins with a roundoff back handspring onto the table followed by 2 1/2 twists. She seemed to change her mind in mid-air, doing just 1 1/2 twist instead.
She walked off the podium and was tended to by team doctor Marcia Faustin before making her way out of the arena.
Biles arrived in Tokyo as the unquestioned star of the Games but struggled, at least by her high standards, during qualifying. In a social media post on Monday, she admitted she felt like the weight of the world was on her shoulders and that the Olympics “were no joke.”
Biles won five medals in Rio de Janeiro five years ago and had a chance to actually top that after advancing to all five finals. It remains to be seen whether she will be available for the all-around final on Thursday night and the event finals later in the Games.
After two rotations, the United States trails ROC 2.5 points.