The assault happened in August at the Top Dog Tavern on Outer Highway 10 in Yucaipa after the bar closed.
Surveillance video shows a group of people standing around in the parking lot when apparently an argument ensues.
One man throws a punch, hitting the victim in the head and knocking him to the ground.
Police are hoping witnesses or anyone with information about the suspect will come forward.
Anyone with information is asked to call the Yucaipa Police Department Detective Division at (909)918-2305. Anonymous information can be provided to WeTip at 1-800-78-CRIME or www.wetip.com.