The Glazer family, who bought the club for £790m in 2005, announced they were considering selling in November.

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

The second stage ended last month with uncertainty over whether the process had reached the point of exclusivity being granted.

It is understood the Glazer family, who said they were considering selling to "explore strategic alternatives", have now opted to extend the process.

This means potential purchasers, either of the whole club or just a partial stake - an option believed to be appealing to bidders from Elliott Investments - must put more offers forward in the hope of concluding a deal.

It had been initially hoped the process being run by the Raine Group would be completed by the end of the season, but the additional time for new bids means that is now unlikely to happen.

Sheikh Jassim will be expected to submit a new bid to buy 100% of the club, with Ratcliffe having followed a strategy of attempting to purchase the Glazer family's 69% shareholding.

The Glazer family do have the option of retaining ownership, although the finance required to improve stadium infrastructure would be brought into sharp focus if, as expected, Old Trafford misses out on being part of the UK and Ireland's bid to host Euro 2028. Manchester City's Etihad Stadium and Everton's new ground are predicted to be the north west stadiums chosen.

It is estimated rebuilding Old Trafford on its current site would cost a minimum £1bn.