German Gorbuntsov was shot by a man armed with a sub-machine gun as he entered a block of flats in Byng Street, Isle of Dogs, on Tuesday.
The Metropolitan Police are treating the shooting as attempted murder.
The suspect is a white male who ran off along Westferry Road. Mr Gorbuntsov is said to be critical but stable and is being kept under armed guard.
A spokesman for the Metropolitan Police, who have not officially confirmed Mr Gorbuntsov’s identity, said detectives from the Trident Gang Crime Command were dealing with the incident which happened at about 19:30 GMT.
“This is sitting with Trident which investigates gang-related shootings,” he said.
Mr Gorbuntsov, who is in his 40s, previously owned banks in Russia and Moldova, according to Russian media.
He was returning to his home when the attacker opened fire, the Russian Kommersant newspaper has reported. He is in coma but police have said he is in a stable condition.
Scotland Yard declined to reveal where Mr Gorbuntsov was being treated. No arrests have been made.
There has been speculation in the Russian press that Mr Gorbuntsov was a witness to a murder attempt on another Russian banker, Alexander Antonov, in Moscow in 2009.
Aleksander Nekrassov, a former Kremlin advisor, told the BBC: “It looks like a contract hit to be honest because a sub-machine gun is not really a weapon that would be used by some amateur.
“What is important is that Mr Gorbuntsov has been saying publicly through his lawyer, which was in the papers in Russia, that he might actually know of people who might have been linked to this attempted assassination [on Mr Antonov], so we might conclude that it has some sort of a link on this attack on him.
“Certain people were either trying to avenge or interfere with a criminal investigation. I think what we are seeing here is [the] strange ways that some of Russian businessmen carry out their deals, spilling over into Britain.”