The giant American financial investor Carlyle is in talks about a major investment in Manchester United Football Club as the auction of the Premier League side nears its concluding stages.

Sky News has learnt that Carlyle is among a handful of parties which have pitched proposals to acquire a minority stake in the Old Trafford outfit.

Carlyle, which has assets of more than $370bn (£298bn) under management, ranks among the world's largest private equity firms.

In the UK, it has owned companies including the RAC breakdown recovery service, and Addison Lee, the taxi-hire group.

One source close to the situation said this weekend that Carlyle's interest in Manchester United was "serious", adding that it had been engaged in discussions for some time.

Nevertheless, key details of Carlyle's proposal, including the amount of capital it would look to deploy and the structure of a deal, have yet to be finalised.

Carlyle declined to comment.

Deadline set for final proposals

Carlyle's interest has emerged a fortnight before a deadline set by Raine Group, the advisers handling the sale process, for final proposals to acquire or invest in Manchester United.

Sky News exclusively revealed last November the Glazer family's plan to explore a strategic review of the club its members have controlled since 2005, kicking off a five-month battle to buy it.

Since then, dozens of parties have been rumoured or reported to have shown an interest, although few have emerged as genuinely credible bidders.

A bid deadline of 28 April has been set by The Raine Group, the merchant bank handling the sale, and which oversaw last year's £2.5bn takeover of Chelsea by a consortium led by Todd Boehly and Clearlake Capital.

The culmination of the process comes as United chase trophies in both the FA Cup, with a semi-final against Brighton and Hove Albion next weekend and the second leg of a Europa League quarter-final against Sevilla to come, with the tie finely poised at 2-2.

In February, the Red Devils' 2-0 defeat of Newcastle United in the Carabao Cup final landed their first trophy for six years.

Who's in contention?

The two parties which remain in contention to buy out the Glazers altogether are Sheikh Jassim bin Hamad al-Thani, a Qatari businessman who chairs the Gulf state's Qatar Islamic Bank; and Ineos Sports, part of the petrochemicals group owned by Sir Jim Ratcliffe.

Both have reportedly tabled offers below a £6bn figure, which has been speculatively touted as the Glazers' asking price for the club they bought in 2005 for less than £800m.

In addition, several financial investors have shown interest in becoming minority shareholders or providing some form of structured finance to the club to allow it to revamp the ageing infrastructure of its Old Trafford home and Carrington training ground.

Those which have lodged minority investment proposals with Raine include Elliott Management, the American hedge fund which until recently owned AC Milan; Ares Management Corporation, a US-based alternative investment group; and Sixth Street, which recently bought a 25% stake in the long-term La Liga broadcasting rights to FC Barcelona.

At a valuation of £5bn - below the Glazers' rumoured asking price - a sale of Manchester United would become the biggest sports club deal in history.

It would eclipse even the $6bn (£4.8bn) takeover of the Washington Commanders NFL team agreed this week by Josh Harris, an American private equity billionaire.

Part of the lure of such a valuation resides in potential future control of the club's lucrative broadcast rights, according to bankers, alongside a belief that arguably the world's most famous sports brand can be commercially exploited more effectively.

On Friday, New York-listed shares in Manchester United closed down nearly 5% at $22.02, giving the club a market valuation of close to $3.8bn (£3.1bn).

Glazers told to sell 'without further delay'

This week, Manchester United's largest fans' group, the Manchester United Supporters Trust (MUST), called for the conclusion of the auction "without further delay".

"When it was announced in November that the Glazers were undertaking a 'strategic review' and inviting offers to buy the club, MUST welcomed the news and went on to urge the majority owners to move ahead with the process with speed, so that any period of uncertainty was as short as possible, it said in a statement.

"Nearly five months on, we read speculation that offers from prospective buyers remain below the Glazers valuation, and that a third round of offers will now be invited.

"With Erik ten Hag having made such great progress in his first season, and with the vital summer transfer window a matter of weeks away, the news of these delays and further prolonged uncertainty are of great concern."

The Glazers' 18-year tenure has been dogged by controversy and protests, with the lack of a Premier League title since Sir Alex Ferguson's retirement as manager in 2013 fuelling fans' anger at the debt-fuelled nature of their takeover.

Fury at its participation in the ill-fated European Super League crystallised supporters' desire for new owners to replace the Glazers, although a sale to state-affiliated Middle Eastern investors would - like Newcastle United's Saudi-led takeover - not be without controversy.

Confirming the launch of the strategic review in November, United's executive co-chairmen, Avram Glazer and Joel Glazer, said: "The strength of Manchester United rests on the passion and loyalty of our global community of 1.1bn fans and followers.

"We will evaluate all options to ensure that we best serve our fans and that Manchester United maximizes the significant growth opportunities available to the club today and in the future."

The Glazers listed a minority stake in the company in New York in 2012 but retained overwhelming control through a dual-class share structure, which means they hold almost all voting rights.

For the last two years, the club has been promising to introduce a modestly sized supporter ownership scheme that would give fans shares with the same structure of voting rights as the Glazers.

The initiative has, however, yet to be launched despite a pledge to have it operational by the start of the 2021-22 season.

"Love United, Hate Glazers" has become a familiar refrain during their tenure, with supporters critical of a perceived lack of investment in the club, even as the owners have taken huge dividends as a result of its continued commercial success.