A 30-year-old man was hit in the face and needed hospital treatment for a broken nose.
The attack is said to have occurred at Yates on Woodhouse Lane, near to the toilet area at the back of the venue at 3.15am on Sunday, July 31.
After the incident the suspect left but returned a short time later and was involved in another altercation with a group of people outside the bar.
Officers want to speak to the man, pictured, in connection with the incident. He is described as white, slim and was wearing a black coloured T-shirt with a Vivienne Westwood motif on the front.
Any witnesses are asked to call Leeds CID on 101 quoting crime number 13160327915.