Roman Abramovich has owned Premier League club Chelsea since 2003
The government is set to approve Chelsea's £4.25bn sale in the next 24 hours, BBC Sport has learned.
However, the deal "still has major hurdles to overcome" according to a senior Whitehall insider.
It is understood that, because owner Roman Abramovich has a Portuguese passport, the takeover needs to be licensed by authorities in that country too.
Ministers are now said to be in "intense discussions" with their counterparts at the European Commission to provide them the assurances they need to approve the deal.
Chelsea have agreed terms on a deal with a private-equity funded consortium led by US investor Todd Boehly, co-owner of the LA Dodgers baseball team.
The club was put up for sale before owner Abramovich was sanctioned for his alleged links to Russian president Vladimir Putin following the invasion of Ukraine.
The government then issued a special licence for Chelsea to continue to operate, which expires on 31 May.
Last week the BBC learned that the government was worried the deal may be at risk of "falling apart" due to a lack of consensus with the club over the proceeds of any sale.
The government version of events was disputed by sources close to Abramovich when approached.
However Abramovich is now understood to have provided legally binding guarantees that a £1.6bn loan to the club will not go to the Russian oligarch or his family. This would allow the money to go into a frozen account under government control.
"Everyone wants to get the deal done, but with the complicated nature of the deal and the Chelsea ownership structures, nothing is simple," said the Whitehall source.
"We are working hard to assure our international partners who rightly want their own assurances on this deal and of course how the proceeds will eventually be spent.
"Time is rapidly running out, this deal has to get done by the end of Tuesday, otherwise major football deadlines may be missed and the club will be at risk."
The Football Association needs to nominate clubs for Uefa competition by the start of next month. The Premier League meets on 9 June to hand out licenses for next season.
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Source: bbc.com