Former U.S. national team gymnast Maggie Nichols says that she, too, was sexually assaulted by former Team USA physician Larry Nassar, writing in a letter that she was the first gymnast to alert USA Gymnastics officials about Nassar's criminal behavior.

Nichols revealed the abuse in a letter she plans to submit to an Ingham County, Michigan, judge who will preside over Nassar's sentencing hearing in Lansing on Jan. 16.

"Up until now, I was identified as Athlete A by USA gymnastics, the US Olympic Committee and Michigan State University. I want everyone to know that he did not do this to Athlete A, he did it to Maggie Nichols," Nichols wrote.

Nichols competed as an elite-level gymnast by age 13. At 14, she made the U.S. women's national team. She retired from elite competition after narrowly missing the 2016 Olympic team, in large part due to a meniscus tear in the months leading up to the Olympic trials.

She wrote in her letter that Nassar initially treated her for an elbow injury but then, when she was 15, for severe back pain.

"I started to have back problems while at a National Team Camp at the Karolyi Ranch. This is when the changes in his medical treatments occurred," Nichols wrote. "I remember he took me into the training room, closed the door and closed the blinds. At the time I thought this was kind of weird but figured it must be okay ... but then he started touching me in places I really didn't think he should."

Gymnast Maggie Nichols has accused former U.S. gymnastics doctor Larry Nassar of sexual abuse and says she was the first to alert USA Gymnastics officials about Nassar's criminal behavior. Mark Buckner/NCAA Photos/Getty Images

Nichols said Nassar performed the treatments without gloves, without anyone else in the room and without explaining the reasoning behind his methods, echoing allegations raised by several other former Team USA gymnasts.

Former Olympic gymnasts Aly Raisman, McKayla Maroney and Gabby Douglas have all come forward in recent months alleging Nassar sexually assaulted them during medical exams. They are all members of the so-called Fierce Five, the gold-medal-winning team from the 2012 London Olympics,

Nichols wrote that she and her coach reported Nassar to USA Gymnastics leadership in the summer of 2015.

"One day at practice, I was talking to my teammate, and brought up Dr. Nassar and his treatments. When I was talking to her, my coach overheard. I had never told my coach about these treatments. After hearing our conversation she asked me more questions about it and said it doesn't seem right ... so she did the right thing and reported this abuse to the USA Gymnastics staff," Nichols wrote.

ESPN has learned that USA Gymnastics contacted the FBI about Nassar in the summer of 2015 but never alerted anyone at Michigan State about the allegations against him. An osteopathic physician at Michigan State, Nassar continued to treat patients at the university until a wave of similar reports in late 2016 led to his dismissal.

In November, Nassar pleaded guilty to 10 counts of criminal sexual conduct. Last month, he was sentenced to 60 years in prison on federal child pornography charges. Next week, in a Lansing courtroom, the judge in one of Nassar's Michigan-based cases has set aside four days for any woman alleging abuse by Nassar to address the court.

Nichols is now 20 and competing as a sophomore at Oklahoma, where she became just the ninth gymnast in NCAA history to notch the rare "GymSlam" by earning perfect 10.0 scores on every apparatus and helped the Sooners to the 2017 national title. She said she decided to share her story publicly to empower and inform other athletes.

"Not only was Larry Nassar my doctor, I thought he was my friend. He contacted me on Facebook complimenting me and telling me how beautiful I looked on numerous occasions. But I was only 15 and I just thought he was trying to be nice to me. Now I believe this was part of the grooming process I recently learned about," Nichols wrote. "We were subjected to Dr. Nassar at every National Team Camp which occurred monthly at the Karolyi Ranch. His job was to care for our health and treat our injuries. Instead, he violated our innocence."

John Barr is an investigative reporter for ESPN.