Officers are still appealing for witnesses to the incident which occurred at the entrance to the travelling fair near York Racecourse.
A 15-year-old boy and an 18-year-old man, who were arrested in connection with the assault, remain on police bail as enquiries continue.
The victim suffered serious head injuries when he was assaulted at the entrance to the travelling fair, on Knavesmire Road, near York Racecourse at around 10pm on Saturday 17 September 2011.
He was taken in a critical condition in Leeds General Infirmary.
Anyone who can help the police with the investigation are urged to contact York CID on 0845 60 60 24 7, quoting reference number 12110158476. Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.