The 28-year-old man was assault in Digital bar on Wellington Street in the early hours of Saturday morning (11 October).
The man was with friends in the bar when for reasons unknown, both he and one of his friends were attacked by a man at approximately 1.50am.
The 28-year-old was knocked unconscious as a result of the attack and remains in hospital in an induced coma but in a stable condition. His 30-year-old friend sustained injuries to his face.
Police are appealing to anyone who may have been in the bar at the time or who witnessed the assault to contact police on 101, or Crimestoppers on 0800 555111, quoting incident number 103 of 11 October 2014.