"It was a small tussle, nothing serious," police spokesman Marcel Bright said. "He refused to be handcuffed."
The incident occurred around 2:30 a.m. near the Leg Room, a bar in Chicago's Gold Coast neighborhood, Bright said.
Gilmore was arrested for trespassing, resisting arrest, possession of drug paraphernalia and possession of less than 2½ grams of marijuana. He was released from police custody after posting bond, Bright said.
Gilmore signed with the Bears in 2002 after being cut by New Orleans at the end of his rookie year training camp. The former Penn State player appeared in all 16 regular-season games for Chicago in 2005.
A Bears spokesman did not immediately return a telephone call seeking comment.