Officers were called to the five-star hotel, in Park Lane, Mayfair, at around 5.30pm on Friday (May 1), following reports of an unresponsive man in one of the rooms.
London Ambulance Service also attended and the man, aged in his 40s, was pronounced dead at the scene.
Two men – both known to the deceased – were arrested in connection with the incident. They have been bailed, pending further enquiries, to return to a central London police station in June.
A post-mortem examination, held at Westminster Public Mortuary on Sunday, proved inconclusive.
The coroner has ordered further toxicology tests, which are expected to take around eight weeks.
The Metropolitan Police said the sudden death was being treated as unexplained, adding that it is normal practice for post-mortem examinations to be conducted in such cases.
The man's next of kin have been informed, but the body has yet to be formally identified.
Officers from Westminster are continuing to investigate.