US gymnast Simone Biles praised for her ‘courage and grace’ as she pulls out of yet more Olympic events

US gymnast Simone Biles has withdrawn from the uneven bars and vault finals at the Tokyo Games just hours after complaining that she was suffering from so-called 'twisties', which she says has left her "mind and body out of sync".

Biles, the 24-year-old four-time Olympic champion, caused a stir this week when she announced that she wouldn't be competing in Tuesday's women's team final and Thursday's individual all-around final, citing a need to safeguard her mental health.

Her continuing participation in this summer's Games have now been thrown into further doubt after it was confirmed that she will drop out of two events on Sunday – and she is yet to confirm if she will take part in two further finals on the floor and balance beam, both of which are due to take place next week.

A statement from US Gymnastics confirmed Biles' withdrawal, adding that the star would continue to be "evaluated daily".

"After further consultation with medical staff, Simone Biles has decided to withdraw from the event finals for vault and the uneven bars," the statement said.

"MyKayla Skinner, who had the fourth-highest score in vault during qualifications, will compete in vault finals for the US alongside Jade Carey, who finished with the second-highest score.

"We remain in awe of Simone, who continues to handle this situation with courage and grace, and all of the athletes who have stepped up during these unexpected circumstances."

The development comes just hours after Biles confessing on social media that she was suffering from 'twisties' – a term used in gymnastics to describe an athlete who is suffering from a mental block which hinders their ability to perform.

She also published a video to Instagram which showed her struggling to land on her feet after performing two sets on the high bars.

"After the performance I did, I just didn't want to go on," said Biles earlier this week after she withdrew from events having tallied her lowest-ever Olympic score in the opening rotation.

"I have to focus on my mental health. I just think mental health is more prevalent in sports right now.

"We have to protect our minds and our bodies and not just go out and do what the world wants us to do.

"I don't trust myself as much anymore. Maybe it's getting older. There were a couple of days when everybody tweets you and you feel the weight of the world.

"We're not just athletes. We're people at the end of the day and sometimes you just have to step back."

Biles, who was favored to win gold in every event in which she was due to compete, also said that she has no idea how long her bout of 'twisties' will last – and added that gymnastics can be a tremendously dangerous sport if an athlete enters competition on uncertain ground.

With Biles set to compete again on Monday, all eyes will be on the sport's biggest star amid questions about whether her Olympic Games campaign was over before it ever really began.