Sheikh Jassim and Ineos owner Sir Jim Ratcliffe are the only known bidders aiming to buy the club, while Finnish businessman Thomas Zilliacus has also expressed interest.

But talks have also taken place with a number of parties about buying a partial stake.

Interest from former AC Milan owners Elliott Investment Management has been known for some time, while US investor Sixth Street was reported to still be interested despite denying claims of involvement in the process in January.

Respected sources have also suggested Ares Management is keen on making some kind of investment, while BBC Sport has established that Carlyle has also spoken to the Raine Group.

It is understood Carlyle's involvement would be to buy a stake in the club rather than merely provide financing. Financing would only add to United's debt, which in their recently published second-quarter results stood at almost £1bn.

The process to explore "strategic alternatives" for United began in November, when the Glazer family, who bought the club for £790m in 2005, announced they were considering selling.

The Americans have established a valuation of £5-6bn.

Interested parties have been asked to submit a third round of proposals by the end of this month.

It is not clear whether the Glazer family will sell the club or retain control.

However, confirmation this week that Old Trafford will not host matches at Euro 2028 despite having the largest capacity of any ground in England apart from Wembley has once again brought into focus the amount required to modernise the ground.

It is estimated that cost would be at least £1bn, with some arguing a better option would be to build a new ground close to the current one, as Tottenham decided to do.

Carlyle has declined to comment on its interest in the process.