The battle to buy Manchester United heated up on Wednesday as Qatari banker Sheikh Jassim Bin Hamad Al Thani and British billionaire Jim Ratcliffe prepared to raise their bids for the 20-time English champions.

Both parties were expected to increase their initial offers after the submission deadline of 2100 GMT was extended by merchant bank Raine, which is assisting with the sale of the club, following confusion over the timing, the BBC reported.

Sky Sports also reported that Sheikh Jassim and Ratcliffe had been granted extensions to submit fresh bids.

The new deadline for offers has not been made clear, according to the BBC.

United's owners, the Glazer family, have reportedly set a world record £6 billion ($7.3 billion) valuation for a sports club.

Sheikh Jassim's bid for 100 percent control of the club promises to wipe United's $620 million debt and invest in a new stadium and training ground, in addition to backing for the men's and women's teams.

A source close to Sheikh Jassim's bid told AFP he remains confident his bid is "the best for the club, fans and local community."

INEOS chemical company founder Ratcliffe, a boyhood United fan, has been more circumspect in his assessment, insisting he will not pay a "stupid" price in a bidding war for one of football's most iconic clubs.

"How do you decide the price of a painting? How do you decide the price of a house? It's not related to how much it cost to build or how much it cost to paint," Ratcliffe told the Wall Street Journal this week.

"What you don't want to do is pay stupid prices for things because then you regret it subsequently."

Ratcliffe, who wants the 69 percent stake owned by the Glazer family, said his interest in United would be "purely in winning things", calling the club a "community asset".

Deeply unpopular with supporters since they saddled the club with debt in a £790 million leveraged takeover in 2005, the Glazers appeared ready to cash out at an enormous profit when they invited external investment in November.

However, they could yet shun the option of selling a controlling stake in the club, with other parties interested in a minority shareholding.

The initial offers from the first round of bidding last month were believed to have been worth around £4.5 billion.

That would surpass the Premier League record of £2.5 billion paid for Chelsea last year by a consortium led by LA Dodgers co-owner Todd Boehly and private equity firm Clearlake Capital, with a further £1.75 billion promised in investment in infrastructure and players.

Bidders are expected to hear from United next week, with another round of bidding still in play.

If one bid is vastly ahead of the others, it could be chosen to enter into a period of exclusivity, which would allow further negotiation ahead of a final sale.

- Qatar eyes Premier League status -

Ratcliffe visited Old Trafford last Friday along with INEOS representatives, a day after a delegation from Sheikh Jassim's group toured the club's stadium and training ground to hold more talks as part of their due diligence.

Just months after hosting the 2022 World Cup, a successful Qatari bid would give the Gulf state pride of place in the Premier League -- the world's most-watched domestic competition.

But it would also be controversial.

Sheikh Jassim is the son of former Qatari prime minister Sheikh Hamad bin Jassim bin Jaber Al Thani, and his close links to the gulf state's ruling elite would raise questions over another Premier League club becoming a state-backed project.

Premier League champions Manchester City's fortunes have been transformed since a takeover from Sheikh Mansour, a member of Abu Dhabi's ruling family in 2008.

In 2021, the Saudi sovereign wealth fund bought a controlling stake in Newcastle.

Amnesty International has called on the Premier League to tighten ownership rules to ensure they are "not an opportunity for more sportswashing."

United, three-time European champions, haven't won the Premier League since legendary boss Alex Ferguson led them to a 20th English title in his final season before retiring in 2013.

But they are enjoying a renaissance under Erik ten Hag's management this season and ended a six-year trophy drought by lifting the League Cup last month.