Simone Biles said she had put her "mental health first" after missing out on adding a fifth Olympic gold medal to her collection following an early withdrawal from the women’s team final.
The 24-year-old gymnastics icon revealed she was “dealing with things internally” after a disappointing performance on the vault.
Biles posted the lowest score of the first rotation on Tuesday as she landed awkwardly after failing to execute an Amanar, while only completing a Yurchenko 1.5 twist.
After she subsequently withdrew, Team USA had to settle for a silver medal behind the Russian Olympic Committee while Great Britain completed the podium.
Biles admitted that she was "fighting demons", explaining: "I just don't trust myself as much as I used to. I don't know if it's age. I'm a little bit more nervous when I do gymnastics. I feel like I'm also not having as much fun."
She added: "I say, 'put mental health first'. Because if you don't, you won't enjoy sport and won't succeed as much as you want to.
"So it's okay sometimes to sit out the big competitions to focus on yourself, because it shows how strong a competitor and person that you really are, rather than just battling through it."
The big names continue to tumble in the women’s singles tennis event, with second seed Naomi Osaka defeated in straight sets.
The home favourite, who lit the Olympic cauldron on Friday, was denied a place in the quarter-finals after being ousted 6-1 6-4 by world number 42 Marketa Vondrousova.
This event marked Osaka’s first competitive tennis in two months since her early withdrawal from the French Open at the end of May, citing mental health issues.
The world number two is the latest of the big names to fall at the Tokyo Games, with top seed Ash Barty and third seed Aryna Sabalenka also suffering early exits.
"Of course, it's one of the biggest wins of my career," Vondrousova said. "Naomi is a great player, so I knew it would be a tough match.
“I'm very happy with my play. I played amazingly in the first set, and then the second set was really tough. I'm just happy to be through."
ARGENTINA RECOVER TO SEE OFF SPRINGBOKS
Argentina recovered from a dreadful start to beat South Africa and book their place in the rugby seven semi-finals.
Trailing 7-0 after just under two minutes, the Pumas were then reduced to six men when Gaston Revol - who was reduced to tears - was shown a straight red card.
Nevertheless, they demonstrated tremendous resilience and character before eventually running out 19-14 winners.
Argentina will play Fiji in the last four after the reigning Olympic champions swept Australia aside 19-0.
Great Britain stormed back from 21-0 down to beat the USA, scoring four tries to secure a dramatic 26-21 victory.
Team GB will play New Zealand, who eased to a 21-10 success over Canada.
NYIKA BITES BACK
New Zealand's David Nyika escaped with his right ear intact after a shocking biting incident that saw his Moroccan rival Youness Baalla come under fire.
The incident, which occurred in round three of the last-16 heavyweight showdown that Nyika won on each judge's card, was strikingly similar to the moment when Mike Tyson bit a chunk off Evander Holyfield's left ear during their 1997 world title clash.
"Luckily he didn't get a mouthful of me. He had his mouth guard on and I was a bit sweaty," Nyika said.
"The heat of battle can bring the best and the worst out of people.
"This is part of sport. I have nothing but respect for my opponent and can appreciate the frustration he must have felt."