The individual all-around Olympic competition is gymnastic’s premier event, but the sport’s top star will not be participating in it. Simone Biles, a four-time gold medal winner, has withdrawn from the Thursday competition, citing mental health concerns.

Biles had withdrawn from a team event on Tuesday after she lost confidence in her ability to execute her gravity-defying routines. She was afraid a poor performance would cost her teammates a chance at a medal. In her absence, they won silver.

“We wholeheartedly support Simone’s decision and applaud her bravery in prioritizing her well-being,” USA Gymnastics said in statement. “Her courage shows, yet again, while she is a role model for so many.”

Biles is the most dominant gymnast in history. She hasn’t lost an all-around competition since 2013.

“At the end of the day, we’re human, too, so we have to protect our mind and our body rather than just go out there and do what the world wants us to do,” Biles explained on Tuesday. “With the year that it’s been, I’m really not surprised how it played out.”

“Whenever you get in a high stress situation you kind of freak out,” she added. “I have to focus on my mental health and not jeopardize my health and wellbeing.”

The New York Times provides more details:

While she had come to the Tokyo Olympics feeling “pretty good,” the weight of expectations on her as Team U.S.A.’s biggest star at the Tokyo Games became tougher by the day, and in the hours before the team final she said she was shaking and couldn’t nap. In the end, the pressure was just too heavy for her to bear, she said after withdrawing from the team final on Thursday.

Biles might still compete in individual event finals. She’s qualified for all four – floor, vault, uneven bars, and beam.

Biles has been widely praised for her decision to prioritize her mental health. Aly Raisman, the captain of America’s 2012 & 2016 women’s Olympic gymnastics teams tweeted, “Just a friendly reminder: Olympic athletes are human & they’re doing the best they can. It’s REALLY hard to peak at the right moment & do the routine of your life under such pressure. Really hard.”