One man was assaulted by another at The Sanctuary Bar in St Nicholas Street at around 1.30am on Saturday, October 13.
A North Yorkshire Police spokesman today said: "The victim was head butted, punched and kicked a number of times and required ambulance treatment.
"Officers are asking members of the public to get in touch if they recognise the male in the images as they believe he will have information that will help the investigation."
Anyone with any information is asked to email [email protected] or contact North Yorkshire Police on 101, select option 2 and ask for Tom Eaglestone.
Information can also be passed on anonymously via the independent charity Crimestoppers on 0800 555 111.
Please quote reference number 12180191420 when passing on information.