Glushkov came to the United Kingdom after being freed from prison and spoke out against Berezovsky's death claiming he never believed his friend died of natural causes.
Mr Glushkov was discovered by his family and friends at his house in New Maldon, in London's south-west, late on Monday night, aged 68, the Guardian said.
"There is no evidence to suggest a link to the incident in Salisbury", the Metropolitan Police said in a statement.
Police were called at 2246 GMT (6.46 p.m. ET) on Monday to a residential address in Clarence Avenue, New Malden, where a man in his 60s was found dead.
The death of a 69-year-old Russian man in London is being investigated by counter-terrorism police, Scotland Yard has said.
Glushkov's death came a week and a day after fellow Russian exile Sergei Skripal and his daughter Yulia were critically injured in a nerve agent attack in Salisbury.More news: United Nations officials blast Facebook over spread of Rohingya hate speech
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PUTIN critic Nikolai Glushkov feared being on a Russian hit-list five years before he was found dead with "strangulation marks" on his neck. His family has been informed and a post-mortem examination will be held in due course.
The Guardian reported that Glushkov was close friends with Boris Berezovsky who fled to the United Kingdom in 1999 after falling out with the Russian president.
Glushkov had worked for Russian airline Aeroflot and at Berezovksy's LogoVAZ auto company.
Glushkov said: "You have the deaths of Boris and Badri over a short period of time".
In March 2013, Berezovsky was found hanged in his ex-wife's home.
Speaking to the Guardian at the time, Glushkov said he was extremely sceptical that Berezovsky took his own life, claiming that he was "killed".