The suspect and victim were seen arguing outside the club, in Bath Street, at about 02:30 on Sunday before the assault occurred, police officers said.
Members of the public intervened and the alleged attacker walked off towards West’s Centre with two women.
He is described as being of slim build, with dark hair and stubble.
He was wearing a black NY Yankees baseball cap on backwards, a lighter coloured unbuttoned shirt, possibly denim, with a dark coloured hood and a black T-shirt underneath, blue jeans, and white trainers.
Anyone with information is being asked to phone the police on 612612 or contact Crimestoppers on 0800 555 111 or via the charity’s anonymous online form at Crimestoppers-uk.org.
