Two-time Grand Slam mixed doubles champion Justin Gimelstob has pleaded not guilty to a charge of battery causing serious bodily injury in a Los Angeles court.
Gimelstob, 41, partnered Venus Williams to win the Australian and French Opens in 1998 and twice reached the men's doubles quarter-finals at Wimbledon.
The American will return to court on 31 January to face trial.
He could be sentenced to four years in prison if convicted.
Former friend Randall Kaplan alleges that early in the evening of 31 October, Gimelstob "punched him in the head and face more than 50 times".
Gimelstob's lawyer is Shawn Holley, who was once part of OJ Simpson's defence team.
The judge ordered him to stay away from Kaplan and his wife until his next court appearance.
Since retiring from playing, Gimelstob has worked as a coach and TV commentator and is also a player representative on the ATP Board, where he has served for 10 years.
The players' council, currently led by Novak Djokovic, has the power to remove him, but would need the consent of at least six of its 10 members.