Just after 4am on Friday morning, the 44-year-old man was subjected to a serious assault as he walked along Cromer Street.
The man sustained a serious chest injury and cuts to his upper body after unknown people kicked and punched him, causing him to fall to the ground. The suspects then fled the scene.
The man was taken to York District Hospital for treatment to his injuries.
Police have been carrying out house-to-house enquiries in the area. They are also appealing for anyone who saw or heard anything in the Cromer Street area of the city in the early hours of Friday to contact them.
PC Mark Proctor of York police, said:
This was a nasty, unprovoked assault and I am appealing for anyone who can assist the investigation to contact us as soon as possible.
Anyone who can help the police investigation, is asked to ring North Yorkshire Police on 101, select option 2 and ask for Mark Proctor at York police station.
Alternatively you can pass information anonymously to Crimestoppers on 0800 555 111, quoting reference number 12120122177