The incident happened while the victim was walking near the footbridge of Castle Walk at about 9pm on Tuesday, March 30.
A group of about four or five teenage boys, all white, approached him before one punched him, leaving him with injuries to his face, West Mercia Police said.
Police described the main suspect of the attack as wearing all black clothing at the time.
Anyone with information is urged to contact West Mercia Police on 101, quoting incident reference number 00736i of March 30.
Alternatively, contact Crimestoppers anonymously on 0800555111 or crimestoppers-uk.org