Four-time Olympic champion Simone Biles says she was sexually abused by former Team USA gymnastics sports doctor Larry Nassar.
In an emotional statement, Biles, a star of the Rio Games, said she would not let Nassar "steal my love and joy".
Nassar was jailed for 60 years for possessing child sex abuse images and has also admitted assaulting gymnasts.
"I know this horrific experience does not define me, I am much more than this," said Biles, 20.
Three former US Olympians have accused Nassar of sexual abuse under the guise of medical treatment, including Gabby Douglas, who won gold with Biles in the team event at the 2016 Rio Olympics.
Nassar will be sentenced this month over two cases in which he admits assaulting female gymnasts.
The 54-year-old was jailed in December for three counts relating to child sex abuse images on his computer.
Nassar's lawyers told BBC Sport they would not comment on Biles' statement.
USA Gymnastics said in a statement it was "absolutely heartbroken, sorry and angry that Simone Biles or any of our athletes have been harmed by the horrific acts of Larry Nassar".
'My story will be much greater than this'
Biles, who won four golds and a bronze in Rio, accused Nassar in a post on Twitter headed 'Feelings #MeToo'.
"I too am one of the many survivors that was sexually abused by Larry Nassar," the Texan wrote.
"Most of you know me as a happy, giggly and energetic girl. But lately I've felt broken and the more I try to shut off the voice in my head the louder it screams. I am not afraid to tell my story any more."
She added: "It is impossibly difficult to relive these experiences and it breaks my heart even more to think that as I work towards my dream of competing in Tokyo 2020, I will have to continually return to the same training facility where I was abused.
"I am unique, smart, talented, motivated and passionate. I have promised myself that my story will be much greater than this and I promise all of you that I will never give up.
"I love this sport too much and I have never been a quitter. I won't let one man, and the others that enabled him, to steal my love and joy."
Who else has come forward?
Nassar was involved with the US gymnastics programme from the 1980s until July 2015, when the sport's national governing body sacked him.
More than 130 women have filed civil lawsuits against him alleging abuse.
Olympic gold medallists Aly Raisman and McKayla Maroney are among others to have come forward.
Nassar's case was part of a scandal which saw USA Gymnastics president Steve Penny resign in 2016. Penny was accused by victims of failing to quickly notify authorities about abuse allegations.