The American gymnast McKayla Maroney, an Olympic gold medalist, said she was sexually abused by the same team doctor who is already facing criminal charges for molesting other gymnasts.

Maroney, 21, posted on Twitter early Wednesday morning that the doctor, Lawrence G. Nassar, began molesting her at age 13.

Nassar is in jail in Michigan, facing 22 counts of first-degree criminal sexual conduct involving at least seven other individuals. “This guy is a monster,” Bill Schuette, the attorney general of Michigan, said in February.

Nassar, who has pleaded guilty to possession of child pornography, is awaiting trial on separate criminal sexual conduct charges, and he has been sued by more than 125 women accusing him of sexual abuse. He has pleaded not guilty to the assault charges, and dozens of civil suits filed against him in Michigan are currently in mediation.