GRAND RAPIDS, Mich. -- Imprisoned ex-baseball player Chad Curtis says he's innocent of sexual assault allegations made by three teenagers in a lawsuit.

The $4 million suit filed in federal court in Grand Rapids accuses Curtis of battery and intentional infliction of emotional distress.

The Grand Rapids Press reports Curtis responded on Tuesday in a filing written by his lawyer, Joe Sadler.

Sadler writes that his client "has always maintained his innocence of the charges brought by plaintiffs."

Curtis is serving seven years to 15 years in state prison on a criminal sexual conduct conviction. Curtis was charged with sexually assaulting teen girls in 2012 while working as a volunteer weight-room trainer at a high school.

The 45-year-old played for the Detroit Tigers and five other teams between 1992 and 2001.