Police say the 28-year-old victim went to use a bathroom just off the casino floor at Bally's around 6:00 a.m. when he was followed by the suspect.
Once in the bathroom, police say the robber grabbed the victim from behind and slammed his head into the wall, nearly knocking him unconscious.
The victim fell to the floor where he was punched several more times before $100 was stolen from his pockets.
The attacker then got away.
The victim was taken to the hospital with injuries to his head, nose and face.
Police released a surveillance photo of the suspect on Friday afternoon. The man they are looking for is described as a black male with a muscular build in his late 20s or early 30s. He has a dark complexion, standing about 5'8" to 5'10" tall and weighing around 200 pounds.
If you have any information you are urged to call Atlantic City Police at (609) 347-5780.