The 23-year-old victim was knocked unconscious after being struck from behind outside The Bowery Mission homeless shelter at 227 Bowery just after 2 a.m. Sunday, according to police.
The victim had just left a nearby bar and was on his way to meet friends, according to police.
He was taken to Bellevue Hospital, where he regained consciousness, police said. Nothing was stolen from him, police said.
Police said they believe the attack was unprovoked and is unconnected to the Bowery Mission.
Anyone with information is asked to call Crime Stoppers at (800) 577-TIPS (8477). All calls are strictly confidential.