Dominic Elliott died in hospital on Sunday morning after he was taken ill at the world-famous artist’s house in Bridlington on Saturday.
Today, a Humberside Police spokesman said: “A post-mortem examination was carried out on the body of 23-year-old Dominic Elliott yesterday at Hull Royal Infirmary mortuary and it showed no obvious natural causes for his death.
“Further tests will now be carried out, the results of which will not be known for some weeks.
“Mr Elliott’s family has been fully updated by Humberside Police.”
Officers are continuing to investigate how Mr Elliott became ill before he was taken to Scarborough Hospital by a friend.
Keen sportsman Mr Elliott worked as a personal assistant to the 75-year-old artist, setting up equipment and helping in his studio.
He was the subject of more than one Hockney portrait.
Humberside Police said earlier this week the circumstances of his death were “not clear” but there was no sign of violence.
Hockney, who is not thought to be the friend who drove Mr Elliott to hospital, is said to be extremely upset by the death.
The Bradford-born painter is sometimes referred to as Britain’s greatest living artist and is one of the most influential cultural figures of the last 50 years.
His famous works include A Bigger Splash and the portrait Mr And Mrs Clark And Percy.
As well as his detached house near the seafront in Bridlington, Hockney has homes in London and Los Angeles.
Mr Elliott was a well-known local sportsman and tributes have been paid to him by team-mates at Bridlington Rugby Club and Driffield Hockey Club.