The attack happened outside Club Jalou, in Micklegate, at about midnight.
The victim, 20, was punched once in his face a man in his late teens.
He suffered suffered several fractures to the jaw, a split lip and a bloodied nose and was taken to hospital.
Police said he is still recovering from his injuries after the attack on December 30.
Officers are continuing to investigate the assault and have issued a new appeal today for information.
A spokesperson for North Yorkshire Police said :"We are requesting the public’s assistance to help establish the full circumstances surrounding the incident.
"In particular, we are appealing for anyone who may have witnessed the assault and is willing to provide a statement in relation to the incident."
Anyone with information is asked to call police on 101, quoting reference number 12180002773.