Police are appealing for witnesses after a man was assaulted in Imperial Arcade, off Western Road, Brighton.
The incident took place at about 11.30am on September 1.
A police spokesperson said the 20-year-old victim was taken to Royal Sussex County Hospital in Brighton where he was treated for serious but not life-threatening head injuries, and was later discharged.
It is believed two people may be responsible for the incident, say police.
Anyone who saw what happened, or who saw anyone running away from the arcade area, or who has any further information about the incident, is asked to report it online or call 101, quoting Operation Dulwich.
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111 or report it online.