NEW YORK (CBSNewYork) – The NYPD wants your help identifying a suspect who attacked an East Harlem man in Central Park.

It happened Sept. 22 at 2:30 p.m. near East 106th Street and East Drive.

“The guy, he coming in the bicycle and he hit him and… boom, the guy goes on the floor,” the victim’s friend, Valdez Hipolito, said.

According to police, the victim was walking with his girlfriend when someone came up behind them and smashed him in the back of the head with an unknown object.

Police released a sketch of a suspect who allegedly struck a man in the back of the head in Central Park. (credit: NYPD)

The suspect then rode off on a bicycle toward Madison Avenue, police said.

The victim, 53, suffered a laceration to the back of his head and was rushed to St. Luke’s Hospital, where Hipolito say she remains in critical condition with brain damage.

Police say the victim and suspect don’t know each other, and they’re offering a $2,500 reward for information leading to an arrest.

Anyone with information about this incident is asked to call to call the NYPD’s Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782). You can also submit a tip via the Crime Stoppers website, by tweeting @NYPDTips, or by texting a tip to 274637 (CRIMES) and then enter TIP577.

All calls will be kept confidential.