Mr Berezovsky, 67, was found dead by an employee on Saturday on a bathroom floor at his home in Berkshire.
The examination found nothing to indicate a violent struggle. More tests are to be carried out on the body.
Thames Valley Police said investigations at the property would continue for several days.
They had earlier said there was no evidence so far that a "third party" was involved.
Mr Berezovsky's body was removed from the property in Mill Lane, Ascot overnight on Sunday.
The results of further tests, including toxicology and histology examinations, were likely to take several weeks, police said.
Crime officers have been carrying out forensic examinations at the property and "these are expected to last several days".
"A cordon will remain in place until this work has been completed, to protect the scene," Det Ch Insp Kevin Brown said on Sunday afternoon.
"While this important investigative work continues, we are unable to comment on any items found within the property."
Boris Berezovsky had lived in Britain since 2000Mr Berezovsky's body was reportedly found by an employee, who called an ambulance at 15:18 GMT on Saturday.
He had not been seen since around 22:30 GMT the previous evening.Diminished wealth
Mr Berezovsky emigrated to the UK in 2000.
He amassed a fortune in the 1990s following the privatisation of state assets after the collapse of Soviet communism.
He survived numerous assassination attempts, including a bomb that decapitated his chauffeur.
In 2003 he was granted political asylum in Britain on the grounds that his life would be in danger in Russia.
He was married twice and had six children - two with each of his wives and two with a long-term partner.
The tycoon's wealth is thought to have considerably diminished in recent years, leaving him struggling to pay debts in the wake of costly court cases.
In 2011, Mr Berezovsky reportedly lost more than £100m in a divorce settlement. And, last year, he lost a £3bn ($4.7bn) damages claim against Chelsea Football Club owner Roman Abramovich.
