A 55-year-old man was knocked unconscious during a brutal mugging outside a Brooklyn deli, cops said Thursday.

The victim was standing outside Dean Mini Market on 13th Avenue near 73rd Street in Dyker Heights around 7:45 p.m. Wednesday when a man punched him from behind, causing him to fall to the ground and hit his head, authorities said. 

The heartless robber then continued attacking the victim, kicking him in the head before stealing his wallet and an unknown amount of cash, police said. 

The suspect ran off, heading south on 13th Avenue, cops said. 

The victim was rushed to NYU Langone Hospital-Brooklyn with “serious injuries,” police said. 

His condition Thursday morning was unclear.

Investigators were still looking for the suspect, who wore a gray sweatshirt, light blue jeans, light blue cap and black and white sneakers at the time of the mugging, cops said.