Mr Berezovsky was also a friend of Russian dissident Alexander Litvinenko, who was poisoned with radioactive polonium-210 in London in 2006.
The Met did not name Glushkov, but confirmed they were investigating the death of a man in his 60s in the Kingston borough, which was being treated as unexplained.
Lawyer Andrei Borovkov told Russian media outlets that his client, Nikolai Glushkov, has died, but said he was unaware of the time and circumstances.
The death of a 69-year-old Russian man in London is being investigated by counter-terrorism police, Scotland Yard has said.
It is not yet known how he died but his death has not been linked to the Salisbury poisoning case, the Metropolitan police said.
Police officers man a cordon near where Sergei Skripal was poisoned along with his daughter.
Glushkov was a close friend and business associate of Boris Berezovsky, the Russian oligarch who was found dead at his ex-wife's home in 2013.
At the time of his death, he was living alone in New Malden, south-west London and was said to be a "nice man" who used to give his neighbour's children gifts at Christmas.
"Whilst we believe we know the identity of the deceased, formal identification is yet to take place", police said in a statement. An inquest failed to determine whether he had killed himself or died from foul play.
In the 1990s, Glushkov worked for the state airline, Aeroflot, along with Berezovsky's LogoVaz auto company.
He was arrested in 1999 and put on trial for embezzling US$7 million from Aeroflot.
Nikolai Glushkov, who received political asylum in the United Kingdom, was found dead at his London home on Monday by friends and family. He spent five years in jail and was freed in 2004.
In March last year, he was sentenced to eight years in prison in absentia and issued a one million Russian Ruble fine for allegedly defrauding Aeroflot of $122 million during his tenure as finance director there in the late 1990s.
Last year, Glushkov appeared on a list published by the Russian Embassy in London of Russians wanted for serious crimes whom the United Kingdom had refused to extradite.