The man, who police did not identify, was walking alone in the area of West Sunset and Leighton avenues shortly after midnight when he was accosted by at least two men, all said to be black teens.
The assailants attacked the victim and stole his wallet, containing money and identification, according to department spokesman, Captain Darren McConnell.
Witnesses interrupted the robbery and the assailants fled north on Leighton Avenue. No weapons were believed to have been used in the attack, McConnell said.
The victim was taken to Riverview Medical Center, where he was admitted in serious condition with head and upper-body injuries, McConnell said.
Anyone with information is asked to contact Investigator Wendy Samis of the Red Bank Police Department at 732.530.2700.