A 19-year-old local man suffered a fractured jaw and facial injuries in an incident that occurred in the male toilets at the Tokyo club, Toft Green, between 3am and 3.30am on Sunday 15 July 2012.
The victim received treatment at York District Hospital.
A 19-year-old man, also local, has been arrested in connection with the incident. Following questioning he was released on police bail pending further inquiries.
PC Jon Ayres, of the York Safer Neighbourhood Team, is the investigating officer.
PC Jon Ayres said:
The victim sustained the serious injuries when he exited a cubicle in the male toilets at the Tokyo club in the early hours of Sunday 15 July.
From my inquiries so far, it is believed a number of people were in or around the toilets when the alleged assault occurred.
I am appealing to those individuals to contact me as soon as possible with any information, no matter how small or seemingly insignificant, that could help the investigation.
If you do not wish to contact the police directly, details can be passed on anonymously to Crimestoppers.
Please contact North Yorkshire Police on 101, select option 2, and ask for Jon Ayres.
Alternatively, call Crimestoppers on 0800 555 111 if you want to remain anonymous. Please quote reference number 12120115548.