London 2012 Olympic gold medallist McKayla Maroney has made allegations of sexual assault against former USA gymnastics doctor Dr Larry Nassar.
Maroney posted a lengthy and detailed account on her Twitter page, saying she felt inspired to open up about her experiences.
The 21-year-old American was speaking out as part of the #MeToo movement in the wake of separate complaints against Hollywood film producer Harvey Weinstein.
In the statement, Maroney named Nassar as her alleged abuser, saying incidents had taken place from the age of 13 when she attended a national-team training camp in Texas.
Earlier this year, Nassar pleaded guilty in a US federal court to possessing child-abuse images which were discovered as police investigated allegations against him of assaulting young females.
He is now in prison awaiting trial in Michigan following charges on multiple counts of first-degree criminal sexual conduct. Nassar denies the charges.
Maroney was part of the USA squad which won team gold at London 2012 and she also took individual silver.
Maroney wrote on Twitter: "I was molested by Dr Larry Nassar, the team doctor for the US Women's National Gymnastics Team, and Olympic Team.
"Dr Nassar told me that I was receiving 'medically necessary treatment that he had been performing on patients for over 30 years'.
"It started when I was 13 years old .... and it didn't end until I left the sport.
"It seemed whenever and wherever this man could find the chance, I was 'treated'. It happened in London before my team and I won the gold medal, and it happened before I won my silver."
Maroney also made claims about Nassar's conduct around the 2011 World Gymnastics Championships in Tokyo, allegedly having been given a sleeping pill on a flight and later waking up "all alone with him in his hotel room getting a 'treatment"'. She added: "I thought I was going to die that night."
The American concluded her statement with the message: "Our silence has given the wrong people power for too long, and it's time to take our power back. And remember, it's never too late to speak up."
USA Gymnastics vowed to continue the drive to safeguard its athletes.
In a statement the sport’s governing body in America said: "USA Gymnastics admires the courage of those, like McKayla Maroney, who have come forward to share their personal experiences with sexual abuse. Because of their strength in coming forward, predators can be held accountable for their actions.
"We, like so many others, are outraged and disgusted by the conduct of which Larry Nassar is accused. We are sorry that any athlete has been harmed during her or his gymnastics career."