The last four bidders for Chelsea Football Club have been given extra time to table final offers for the Premier League side, as the most hotly contested sports auction in history looks set to be extended.

Sky News has learnt that the remaining consortia were informed on Thursday by the advisers handling the sale that they must now submit binding takeover proposals in the back half of next week.

The move, which will prolong the next stage of the auction by a small number of days, has emerged less than 24 hours after Chelsea lost the first leg of its Champions League quarter-final 3-1 against Real Madrid, leaving last season's winners on the brink of going out of the competition.

The Chelsea auction has moved at breakneck speed.

A source close to one bidder said they had been told that the final bid deadline had been extended until later in the week in order to give them a full and fair opportunity to adequately finalise the details of their proposals.

The source added that Raine Group, the US merchant bank handling the sale, had also informed them that it is now considering awaiting clearance from the Premier League for all four consortia before presenting a preferred bidder to the government.

Scrutiny of the four bids by English football's top flight has already got under way after the remaining consortia submitted details of their key investors to Raine late last week.

The Premier League is expected to take several weeks to evaluate those involved in the bids - who include a string of US billionaires and pillars of the British corporate establishment - and its work to approve all four of the bidders means the process may need to be extended.

One of the bidders, who spoke on condition of anonymity, said they now anticipated that a final recommendation would be made to ministers later than the original target date of the week beginning 18 April, with the deal now likely to complete in May.

A source close to one of the bidders welcomed the additional time to finalise their bid given the complexity of the process taking place to buy the Blues.

The quartet of bidders comprise: a consortium led by Sir Martin Broughton, the former Liverpool and British Airways chairman; another headed by Todd Boehly, the LA Dodgers part-owner; Steve Pagliuca, owner of the Boston Celtics and a big stake in Atalanta, the Serie A side; and the Chicago Cubs-owning Ricketts family, who have teamed up with Cleveland Cavaliers owner Dan Gilbert and the hedge fund tycoon Ken Griffin.

The four remaining bidders have been holding meetings in London this week with Chelsea board members, staff and Raine as they vie to end Roman Abramovich's 19-year tenure at Stamford Bridge.

They have been told they must provide legal undertakings that they will guarantee at least £1bn of investment in the club's infrastructure if they acquire it in the coming weeks.

The sale process has been complicated by the sanctions against Mr Abramovich and the frenzy of interest in buying last season's Champions League-winners.

Earlier this week, the consortium led by the Ricketts family outlined a series of commitments to Chelsea fans, including a vow never to participate in a revived European Super League project.

Other bidders are understood to have submitted details of commitments to the CST but have chosen not to make them public so far.

The Ricketts-led bid for Chelsea has faced challenges in recent weeks because of a backlash over historical comments made by a family member who is not involved in the offer.

On Thursday, Laura Ricketts made a public statement pledging that Chelsea would "strive to be champions on and off the field" if the family-led group won the auction.

Sky News revealed last week that the fan-led group co-founded by the former Chelsea captain John Terry was in "positive" talks with two of the shortlisted bidders about acquiring a 10% stake.

The four remaining bidders have been holding meetings in London this week

Between them, the final bidders also either control or own stakes in US teams including the Boston Celtics, the Cubs, the LA Dodgers, the Philadelphia 76ers and the Sacramento Kings.

By the standards of conventional takeover processes, the Chelsea auction has moved at breakneck speed, with executives at other major investment banks suggesting that such a complex sale would typically have taken at least six months.

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.

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.

The current Fifa Club World Cup 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.

As well as government consent in the form of a special licence, Chelsea's new owners will also require the approval of the Premier League under its fit and proper ownership test.

None of the bidders contacted by Sky News nor Raine would comment on the amended timetable.