Police released images of a cyclist who critically injured a man by punching him in the back of the head with a chain-wrapped fist on a Midtown street.

The suspect was biking on West 44th Street near Ninth Avenue at about 8:50 p.m. July 26 when he almost collided with a 22-year-old pedestrian, authorities said.

The two got into an argument and the pedestrian tried to walk away, police said.

The crazed cyclist then wrapped a bike chain around his fist and punched the man in the back of the head, police said.

The victim was rushed to Bellevue Hospital in critical condition, authorities said.

The suspect, who was wearing a backpack with the word “RELAY” emblazoned on the back, pedaled away and has not been caught.

Police believe he’s about 5 feet 8 and was last seen riding a blue, 10-speed bike.