THE MAN found on Karon beach was identified late on Saturday night as an American, Jonathan Mark Lemley, 28. He remains in intensive care. His wife is on Phuket.
The man, aged 35 to 40, was discovered on the beach at Karon, south of Patong, about 8am, not far from the landmark lagoon.
His head appeared to have been beaten and his face was also damaged. Nearby were two long sticks, police said.
The man was unconscious and has so far not recovered enough to explain to police who he is or what happened.
There was no identification on him. Parked a short distance away on the sand from where the fair-headed man was found, police found a black Honda motorcycle with the Malaysian registration JQE 4237.
Late today, with the man still in the Phuket City hospital's intensive care unit, Phuket Police Commander Major General Pachara Boonyasit was heading the Karon investigation.
Detectives hope to find some security camera footage that could provide clues to the man's movements.
Thailand has been beset by problems in the tourism sector since the murders of British tourists Hannah Witheridge and David Miller on September 15 on Koh Tao.
That tragedy has since been followed by the drowning of two Indians and two Koreans in separate marine disasters off Phuket's neighboring province of Krabi.