Police are investigating an assault at a licensed-premises in the CBD last month.
Investigators have been told an unknown man approached the victim on level 2 of the Bourke Street club and assaulted him about 3am on 26 October.
The 40-year-old man was treated for non-life threatening facial injuries.
The offender left with a group of people and was last seen walking on Flinders Street.
He is described as 170cm tall, medium build, short cropped black hair and was wearing a red checked shirt.
Police have released images of a man they believe may be able to assist with their enquiries.
Anyone who witnessed the incident or anyone who knows the identity of this man is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au