Pippen, 47, was cooperating with the investigation, sheriff's spokesman Steve Whitmore said. The victim was taking pictures inside Nobu restaurant late Sunday while Pippen dined with his family, said sheriff's Capt. Patrick Davoren.
When Pippen went outside to the parking lot, the man continued to take pictures and sought the Hall-of-Famer's autograph, Davoren said. An argument ensued that led to the altercation, investigators said.
The man was taken to a hospital with a head injury and was treated and released. Investigators were interviewing several witnesses who apparently saw what transpired. Criminal charges could be filed.
"Right now it's under investigation," Whitmore said. "We have to interview everybody to find out what happened."
Inducted into the Basketball Hall of Fame in 2010, Pippen won six NBA titles with Michael Jordan and the Chicago Bulls and was on a list of the league's 50 greatest players announced in 1996.
He is a special adviser to the team's president and chief operating officer. The Bulls declined to comment Monday.