Police were called to the Drink bar, on the Bull Ring, to reports of two men fighting at around 7.15pm but those involved had already left.
Later that evening, officers were called again to the Bull Ring and found the man had been attacked. He suffered non-life threatening injuries. The victim is believed to be one of the men involved in the earlier incident.
Enquiries are still ongoing to trace the second man.
Anyone with information should call officers on 101.