Supporters have held protests outside Old Trafford

US sports tycoon Malcolm Glazer has tabled a fresh offer for the club after two previous bids were rejected.

The plan is thought to include some alterations to the level of debt being put forward to fund the purchase.

But the latest approach is set to spark a fresh wave of campaigns from supporter groups opposed to any deal.

"United fans must wake up and do something before it's too late," said Sean Bones, spokesman for Shareholders United, a group of share-owning supporters.

"It is nothing more than an opportunistic attempt by Malcolm Glazer to make personal gain from an institution which is loved and respected throughout the world, by someone who has no interest in, or respect for, the heritage of the club."

Plans are being made for demonstrations on Sunday at Manchester United's Old Trafford stadium and the Millennium Stadium in Cardiff, where the team will be playing in the FA Cup semi-final.

New players

The part of the plan said to cause the board and supporters most concern is Mr Glazer's reported intention to borrow a sizeable chunk to partly pay for the purchase and then transfer the debt to debt-free United.

The board will have to decide whether their commitment is just to shareholders or to wider 'stakeholders', including supporters Weighing the next move See Man Utd share price

But it is believed the latest deal will include proposals to reduce the debt required to fund the deal from the previous suggested level of �500m.

BBC correspondents say the offer also includes a commitment to provide a �20m transfer fund for new players and backing for the club's plans to expand Old Trafford.

The offer, thought to have been lodged with Manchester United's financial advisers Cazenove at a meeting in London on Thursday, is yet to be formally announced.

Manchester United declined to comment on the reports.

Shares slip

Mr Glazer and his family have been building up their shares in the club over the last 18 months and currently hold a 28.1% stake.

Mr Glazer and his family have been building up their stake in the club

Also the owner of the Tampa Bay Buccaneers American football club, Mr Glazer has proposed to pay �3 per share.

On Friday, shares in Manchester United closed down 5.75p, or 2.09%, at 269.25 pence.

The club's largest shareholders are Irish horseracing tycoons John Magnier and JP McManus, who together hold 28.9% of the club.

They have said they do not intend launching a takeover attempt of their own and are thought likely to be tempted by a cash offer for their shares of about �3 each.