Chelsea owner Roman Abramovich is still waiting for UK authorities to renew his visa which expired last month, a source has told ESPN FC.

Abramovich returned to Russia after his visa ran out and did not attend Saturday's FA Cup final at Wembley, where Eden Hazard's first-half penalty enabled Chelsea to edge out Manchester United and claim the trophy for the eighth time in their history.

A source close to Chelsea told ESPN FC that, while the visa process is taking longer than usual, Abramovich has not had an application for renewal rejected. And the Times reported he has yet to be offered an explanation why UK authorities are taking longer than usual to process the application.

Abramovich's visa situation -- which was first reported in the Financial Times -- comes at a time of heightened tensions between the UK government and Russia following the poisoning of former spy Sergei Skripal and his daughter Yulia in Salisbury back in March, as well as allegations of illegal Russian interference in the lead-up to the Brexit referendum vote.

There have been suggestions that wealthy Russian individuals in London -- of which Abramovich remains the most notable figure -- could be targeted for sanctions by the UK government if relations between the two countries sour further.

Chelsea owner Roman Abramovich watches the team play Arsenal at Stamford Bridge in 2017. Getty

"We do not routinely comment on individual cases," security minister Ben Wallace told the FT when asked about the delay in processing Abramovich's visa request. John Mann, Abramovich's Moscow-based spokesman, told Press Association Sport it was a private matter and there would be no comment.

Having amassed a huge and controversial personal fortune through dealings in the Russian oil industry in the 1990s, Abramovich acquired Chelsea in June 2003 and has invested well in excess of £1 billion in the club, bankrolling a 15-year run that has brought 15 major trophies to Stamford Bridge.

According to the most recent edition of the Sunday Times Rich List, Abramovich is the 13th-richest individual in Britain with a fortune of £9.3bn.

Earlier this month, Abramovich appeared in a Swiss court as part of a 19-year-old legal case aimed to wrest 46 million Swiss francs ($46m) in debts allegedly owed by him and others to a European bank.

Abramovich was in Fribourg court as part of a lawsuit brought by the London-based European Bank for Reconstruction and Development against Abramovich, Russian oil tycoon Eugene Shvidler, and the Russian energy company Gazprom Neft, a bank spokesman said on May 2.

The suit aims to recover alleged debts left behind by Abramovich's now-defunct Runicom trading firm, which was based in Switzerland until its bankruptcy in 2003.

The initial amount sought by EBRD was $17.5m, but the claim has grown to $46m to include interest and costs.

Information from the Associated Press was used in this report