Between 2.05am and 2.15am in the early hours of Saturday morning (15 June 2013), a group of people were involved in an altercation on the Nessgate Corner of Spurriergate.
During the disturbance, the victim, who is believed to be in his late teens, was punched, causing him to fall to the floor where he was unconscious for a period of time. He also sustained a wound to the back of his head which required hospital treatment.
A number of people were involved in the incident and some were seen to walk away from the scene.
Police want to hear from anyone who was in York city centre in the early hours of Saturday and witnessed the incident, or anyone else who has information which could assist the police investigation.
If you prefer to remain anonymous, you can pass information to Crimestoppers on 0800 555 111.
Please quote reference 12130097184.