Chelsea owner Roman Abramovich may be asked to explain the source of his vast fortune before he is granted a new UK visa.
The Russian oligarch, 51, has had to apply for a new investor visa after his previous one expired while he was out of the country.
New rules introduced in 2015 mean he will have to pass a tougher visa test than before, which includes proving that he made his money lawfully.
It comes as the Government is examining investor visas issued to Russians in the wake of the Salisbury nerve agent attack and the deterioration in relations with Moscow.
Downing Street would not be drawn on the circumstances surrounding Mr Abramovich, stressing: "We don't discuss individual cases."
There is nothing to say Mr Abramovich's visa situation, where his renewal application is taking longer than usual, is linked to the strain in relations between Moscow and the West.
The Home Office is examining its approach to the Tier 1 investor route - which requires applicants to be prepared to invest £2 million in the UK - following the nerve agent attack on Sergei Skripal and his daughter Yulia in March.
Visas can currently be rejected if officials believe the applicant obtained money unlawfully or is not in control of funds.
There has been a 84 per cent drop in the number of investor visa applications since the rules were updated, the Guardian reported.
The Prime Minister's official spokesman said: "Work is under way in terms of reviewing Tier 1 investor visas.
"In 2014-15 we took action to tighten up the Tier 1 investor route, including the introduction of new powers to refuse applications where there are reasonable grounds to believe funds have been obtained unlawfully.
"As a result of these reforms applications reduced by 84 per cent.
"We are currently taking another look at how the route operates and are undertaking further checks on investors who came to the UK through this route before the reforms were introduced."
Then home secretary Amber Rudd was questioned about the investor visa route in relation to Russian applicants when she appeared before the Home Affairs Select Committee in March.
Asked if the around 700 existing visas for Russian investors would be reviewed, she told MPs: "I have asked my officials to look at what reforms we might continue with and also to take a look at previous ones over the past few years."
She added: "I have asked to look at the cohort of previous ones to see if there is any action that needs to be taken."