Police are "keeping an open mind" over what may have happened to a man believed to be from Penryn found with serious head injuries outside the Alverton Manor Hotel in Truro at the weekend.
The victim, in his late 20s, was found by a staff member at 7am as they arrived for work on Sunday morning.
Inspector Mark Richards at Truro said CCTV shows the man walking by the Trafalgar roundabout at 12.30am towards the hotel, where he was booked to stay.
However the six-and-a-half hours between then and him being discovered injured are unaccounted for.
Inspector Richards said a Toyota-style vehicle was spotted parked outside the hotel at 6.30am and is appealing for the driver to come forward to help with enquiries.
"We know he was out drinking with friends until about midnight," said Inspector Richards. "We have footage of him walking back to the hotel alone. But we have no sightings after that until he was found collapsed outside.
"We want to know where he was and how he got his injuries."
"We are keeping an open mind," he added. "It is possible he had an accident or fell over."
The man is in a serious condition at Derriford Hospital in Plymouth where he is being treated for a fractured skull and other injuries to his face and brain. He also has injuries to his shoulders and ribs.
Anyone with any information is asked to contact Devon and Cornwall Police on 101 quoting log number 257 of March 3.