Scott Vetere, 39, was arrested with Sydney Blair Townsend, 18, in a car outside an apartment complex in Ann Arbor, Michigan, on October 8.
Police say the pair were engaged in a sex act but will not go into further detail.
Vetere was the teenager's gymnastics coach at The University of Michigan and is a married father-of-three.
Both he and the teenager, who is also a member of the Canadian Senior National Gymnastics team, were arrested for indecent or obscene expose.
They face 90 days in jail and a $500 fine if convicted.
Vetere resigned on October 15, a week after his arrest but has not made a public statement about the allegations.
The university said that he was relieved of his duties two days before he handed in his resignation.
Its officials would not say whether Townsend, who is majoring in sports management, would face discipline.
An investigation has been launched into his conduct, however, a source told DailyMail.com.
She is due to be arraigned on November 5. Vetere was arraigned on October 19. He is next due in court on November 14.
Police in Ann Arbor would not release further details about the case on Wednesday when contacted by DailyMail.com.
The University of Michigan told DailyMail.com that he was immediately suspended after it learned of his arrest.
