The 58-year-old man's death was reported by the masseuse to the Patong hotel's staff, who notified police.
Officers from Kathu Police Station found the man face up on the bed, in his underwear.
The masseuse told police she had been called to the room, gave the man a massage, then he fell asleep. About 6pm, she tried to awaken him and realised he had died.
Phuketwan has the name of the man but will not publish it until relatives have been notified. Police acceded to the hotel's request not to be named.