Covina police say the brutal attack happened on Aug. 17 at Clancy's Sports Bar at 961 N. Azusa.
The victim and suspect were involved in a game of pool just before midnight. After the game, the victim went to the restroom.
Moments later the suspect was seen walking into the restroom holding a beer mug. He was seen on video a short time later leaving the restroom and putting the mug on the ground. He later exited with a female companion.
The victim was hit in the head and knocked unconscious in the restroom, police said.
The possible motive behind the attack was not disclosed.
The suspect was described as a Hispanic man, about 40 years old, standing about 5 feet 6 inches and weighing around 180 pounds, with a mustache. He was wearing a green polo shirt and blue jeans and left in a silver car with paper plates.
Covina police ask anyone with information to call (626)384-5620.