Sky News has learnt that the Ricketts family and Ken Griffin, the Citadel hedge fund billionaire, are in talks to appoint Lazard to advise on their offer for the Stamford Bridge club.

The move comes after days of conjecture that their offer may have been compromised by the backlash against Islamophobic comments made 10 years ago by a member of the Ricketts family.

Raine Group, the investment bank advising on the sale of Chelsea, is understood to be yet to notify the Cubs owners on the fate of their bid, although people close to the process indicated that they may yet join two other serious bidders on the shortlist.

In a statement issued on Friday following a series of talks with Chelsea supporters' groups, Tom Ricketts, the Cubs chairman, said: "My family and I are very grateful to all the fans and supporters' groups who took time to meet with us this week and share their passion and concerns for Chelsea Football Club.

"It's clear you have nothing but the best interests of the club at heart.

"We have listened to all of your feedback - including from the Chelsea Supporters' Trust - and are grateful that the door is still open for us to demonstrate our commitment to working with fans to protect the club's heritage.

"It is now up to us to redouble our efforts and clearly lay out a vision for our stewardship of the club with diversity and inclusion at its heart."

The impending appointment of Lazard as adviser to their bid underlines the Ricketts camp's confidence that it remains a serious competitor in the search for a new owner, who will replace Roman Abramovich as Chelsea's owner after nearly two decades.

A spokesman for the Ricketts-Griffin bid declined to comment on the talks with Lazard.

Stephen Pagliuca, a joint owner of the Boston Celtics basketball team and Atalanta, the Italian football club, has also joined the ranks of those vying to own the Blues.

Sky News revealed on Thursday that a string of bidders including the former US ambassador to the UK, Woody Johnson, and London-based asset manager Centricus had been eliminated from the sale process, and that the leading contenders to buy the club remained consortia led by Todd Boehly, the LA Dodgers part-owner, and Sir Martin Broughton, the former Liverpool FC chairman.

The auction of Chelsea has been transformed into the most hotly contested - and potentially the richest - sale of a leading sports franchise in history, with hundreds of parties expressing an interest in buying a share of the club or controlling it outright.

It emerged earlier this week that Raine had asked bidders to give binding assurances about future spending on the club and its ground before it finalised the shortlist.

At least five existing owners of US basketball and baseball teams have been among the bidders for Chelsea, with Mr Boehly and the Philadelphia 76ers backer Josh Harris - who is part of the bid led by Sir Martin - keen to add the Blues to their collections of sporting assets.

The cluster of American sports billionaires circling Chelsea underlines the extent to which the English Premier League has become a magnet for financiers from across the Atlantic during the last 20 years.

Arsenal, Liverpool and Manchester United have all been acquired by US-based businessmen during that period, and a significant number of other top-flight clubs also have American backing.

A frenzy of bidding among major global investors, billionaires and sports-owners has raised the prospect that Mr Abramovich's original £3bn asking price will be met.

Prior to being sanctioned, Mr Abramovich had said he intended to write off a £1.5bn loan to the club and hand the net proceeds from the sale to a new charity that he would set up to benefit the victims of the war in Ukraine.

The Premier League has disqualified Mr Abramovich from being a director of Chelsea, but has said the move would not affect players' ability to train or fulfil the club's fixtures.

This week, the government agreed to further amendments to a special licence which allows Chelsea to continue operating, enabling it to resume selling tickets for away matches, with the proceeds being held by the Premier League and earmarked for a Ukrainian war victims charity.

Chelsea can also now receive £30m from its parent company to ease cashflow constraints caused by the current crisis.

A rapid sale is seen as essential if Chelsea is to avert the uncertainty that would trigger the break-up of one of the top flight's most valuable playing squads.

Last season's Champions League-winners have been thrown into disarray by Russia's war on Ukraine, with Mr Abramovich initially proposing to place the club in the care of its foundation and then formally putting it up for sale.

Mr Abramovich had initially slapped a £3bn price tag on the Stamford Bridge outfit, with the net proceeds being donated to a charitable foundation set up to benefit the victims of the war in Ukraine.

Whoever buys the club will require the government's consent in the form of a special licence as well as the approval of the Premier League under its fit and proper ownership test.