Police were called to an incident in Garnet Street, Tadcaster at around 5am on Sunday 11 February after a man was found in the road with a head and chest injury.
Although it was first believed that he may have been involved in a collision with a vehicle, following a number of enquiries and initial medical reports, officers are now satisfied that he was not hit by a vehicle.
An investigation is ongoing to establish how the man sustained his injuries.
Anyone who saw anything in the Garnet Street area in the early hours of Sunday morning, or has any information that has not already been passed onto the police should call 101 and pass information to the Force Control Room for incident 12240025597.
The injured man is being treated in hospital for his injuries.