The incident happened at around 1.30am in the early hours of Friday 21 April 2017 in The Pit, The Ginnel and involved a large group of people being asked to leave the premises.
One man, pictured in the CCTV images, remained in the bar and is believed to have directed abusive and insulting words towards the victim.
Officers are appealing for anyone who can help us to identify the man to get in touch as he may have important information that could assist our investigation.
If you wish to remain anonymous, you can pass information to Crimestoppers on 0800 555 111.
Please quote reference number 12170069125 when passing on information.