Simone Biles will not defend her Olympic title in Thursday's individual all-around competition in order to focus on her mental health, USA Gymnastics has confirmed.

The four-time gold medallist from Rio completed only one event in Tuesday's team competition at the Ariake Gymnastics Centre, registering the lowest score of the first rotation.

Biles left the floor with a trainer and, although she later returned donned in a tracksuit, she opted not to continue and remained to support her team-mates who could only secure silver behind the Russian Olympic Committee.

Following the team event, Biles opened up on her struggles at Tokyo 2020 and said she would take it day-by-day before making a decision.

USA Gymnastics subsequently announced she will not participate on Thursday and will continue to be evaluated before a decision is made on whether she takes part in the individual event finals, which take place next week.

"After further medical evaluation, Simone Biles has withdrawn from the final individual all-around competition at the Tokyo Olympic Games, in order to focus on her mental health," a USA Gymnastics statement read.

"Simone will continue to be evaluated daily to determine whether or not to participate in next week’s individual event finals. Jade Carey, who had the ninth highest score in qualifications, will participate in her place in the all-around."

USA Gymnastics hailed Biles for her decision to put her own well-being ahead of competing.

"We wholeheartedly support Simone's decision and applaud her bravery in prioritising her well-being," the governing body added.

"Her courage shows, yet again, why she is a role model for so many."