American superstar gymnast Biles, who won four gold medals in Rio five years ago, has said she is struggling with the "twisties", a condition where gymnasts lose the ability to orientate themselves in mid-air.
She dramatically pulled out of last week's team competition final after one vault as Team USA took silver, and said she feared for her mental health.
The 19-time world champion subsequently withdrew from the all-around final and three of the four apparatus finals -- the floor, vault and uneven bars.
But Biles will be back in the last women's final of the Games, on the beam, and all eyes will be watching to see how she handles the pressure.
Although it is not her strongest apparatus, the 24-year-old is a three-time beam world champion and took Olympic bronze in 2016.
Victory would be one of the great comeback stories, with Biles having documented her mental health struggles during the Games in regular social media posts.
Biles had arrived in Tokyo seeking five gold medals to equal the all-time Olympic record for a female competitor of nine.
The Olympic Stadium is also set for a dramatic day, with potential world-record bids.
Norwegian star Karsten Warholm, who broke a 29-year world record earlier this year, will renew his rivalry with the United States' Rai Benjamin in the 400m hurdles final to close out the morning session.
"I'm excited for the final," said Benjamin, who took silver behind Warholm at the 2019 world championships in Doha.
"It feels great to go through, but the job's not done."
Another world-record holder, Sweden's Armand Duplantis, is a hot favourite for a men's pole vault final which lost some of its lustre with the withdrawal of world champion Sam Kendricks after a positive Covid-19 test.
- Jamaican duo face off again -
The athletics schedule concludes with what promises to be a thrilling women's 200m final.
Jamaicans Elaine Thompson-Herah and Shelly-Ann Fraser-Pryce will go head-to-head again after the former denied her compatriot a record third 100m gold by defending her title on Saturday.
"I just have to go out and run the best race that I can, run and hope that I put myself in a very good position to stand on the podium," said 2012 silver medallist Fraser-Pryce.
Thompson-Herah, who recorded a blistering 21.66secs in Monday's semi-finals, and Fraser-Pryce could be challenged by 2016 400m winner Shaunae Miller-Uibo, rising US star Gabby Thomas and Namibian teenager Christine Mboma.
"I just come here for the experience," said 18-year-old Mboma, who was not allowed to run in the 400m due to elevated testosterone levels.
"I hope to run a good time and get a medal. I just do my best."
Elsewhere, Britain's Jason Kenny will attempt to win his seventh Olympic gold in the men's track cycling team sprint final.
Gold medals are also up for grabs in boxing, canoeing, diving, sailing, weightlifting and wrestling.