The 34-year-old victim was attacked at Vogue nightclub, on King Street/ Spinning Jenny Way, sometime between 2.30am and 4.30am on Sunday 29 December 2013.
He was in the outside smoking area with a friend when he decided to leave the club and walked back into the rear foyer. At that point he was punched in the face from behind without warning or provocation.
Stunned, he fell back and looked round to see who had hit him, but the attacker had fled. His jaw felt numb so he went to hospital where medical staff confirmed it was broken.
As a result of the sudden and unexpected punch, the victim was unable to provide a description of whoever hit him.
PC Peter Stafford, based at Leigh police station, said: “The victim has absolutely no idea why a complete stranger would punch him in the face for no apparent reason.
“He can’t remember upsetting anyone that night or getting into an argument – not that this would justify a violent assault.
“We know for a fact that the club, and the rear foyer – next to the smoking area – specifically, were busy that night so I’m confident someone would have seen this.
“We have spoken to some witnesses but, if you were there and we haven’t spoken to you yet, then please call us.”
Anyone with information is asked to call police on 0161 856 7225 or Crimestoppers on 0800 555 111.