The 43-year-old victim was knocked unconscious when he was punched from behind by an unknown assailant at JD’s sports bar on Commercial Street in Morley.
Police are appealing for witnesses to the incident, which happened in the early hours of Saturday, March 25.
Leeds District CID’s Det Con Simon Goldie said: “We would like to speak to anyone who witnessed this incident in which a man has suffered a serious injury to his jaw after being attacked from behind by an unknown assailant.
“The victim required hospital treatment as a result of the attack and I would very much like to speak with anyone who saw what happened or has information about the attacker.”
Anyone with information is asked to ring Leeds District CID on 101 or Crimestoppers on 0800 555111.