By Bill Wilson
BBC News business reporter
Malcolm Glazer already owns 28.1% of the club
The ongoing drama that is Malcolm Glazer's circling of Manchester United has changed again with the Takeover Panel's decision that he has until midday on Tuesday, 17 May, to "announce a firm intention to make an offer" for the club.
Two weeks ago he submitted revised proposals for an estimated £800m ($1.5bn) takeover of the club to MUFC chief executive David Gill and his fellow directors.
The American had hoped his 300p-a-share package would be enough to sway the board - who previously said the price was "fair" in terms of shareholder value - to recommend the plan to shareholders.
On Thursday the board restated its viewpoint; that the proposal "may be attractive to some shareholders of Manchester United".
But it added: "Given the board's concerns about the potential impact of the proposal on the company, the board has informed Glazer that it cannot provide a recommendation to shareholders to accept any offer made on the basis of the current proposal."
The part of the proposal thought to be causing board and supporters most concern is Mr Glazer's reported intention to borrow a sizeable chunk of money to buy the club and then transfer the debt to debt-free United.
Fans' groups, who have been vociferous in their opposition to the US billionaire, will now be waiting anxiously until the panel's deadline.
"Clearly the Takeover Panel has said it is put-up or shut-up time for Mr Glazer," says Richard Hunter, head of UK equities at Hargreaves Lansdown Stockbrokers.
"The board has come out with an indication reiterating £3 a share is a fair price, but that his proposal leaves the club with debt it has not got at present.
"Mr Glazer has been circling for a while with proposals that may or may not lead to a bid, and the panel has probably decided it is such a high-profile case it is time for him to decide whether he is going to put his cards on the table or not."
It is unclear what the current offer entails, but his previous offers involved transfers of between £300m and £500m of debt and unsubordinated debt to the club.
"Manchester United has never been in a more vulnerable position than it is at present, " says Sean Bones, spokesman for Shareholders United, a fans' group with 28,000 members.
"The latest statement from Manchester United is as close to a rejection as it can get. Now the shareholders have to continue to stand together to see off this threat."
United chairman Sir Roy Gardner, the senior City figure on the board, has intimated before that £300m worth of debt might jeopardise the club's financial future, and lead to a meltdown of the type seen at Leeds United.
Mr Glazer, who already owns 28.1% of the club, had been trying to find ways of soothing supporter anger - but they have rebuffed all attempts to woo them with potential shareholdings.
It might be hard to win over some Manchester United fans
They fear he will raise ticket prices and cut investment to pay back his debt, and also point to the fact that Mr Glazer had no previous interest in soccer.
In February, the United board reluctantly gave the US tycoon, who owns the NFL franchise Tampa Bay Buccaneers, limited access to club accounts.
At the time, the club said it would allow Mr Glazer "limited due diligence" to give him the opportunity to turn the proposal into a formal bid.
"The institutions with a stake in the club think £3 a share is a fair price. There is no financial logic in terms of price which says the club cannot accept it," says Harry Philp, managing director of sports consultancy Inner Circle Sports.
"But the board has had to look at what a Glazer takeover might do structurally to the club's finances. This is a well-run, debt-free, club."
Mr Hunter believes the impasse between the Glazer camp and the club's board may be down to differences of approach over tackling the potentially-lucrative market of the US.
"A Glazer takeover would offer an immediate entry into the US market, which they have been trying to crack for a number of years. It is not really a market they have been able to get their arms around until now.
"I suspect that some of the disagreement between the two sides may be about the best way forward there."
However Mr Hunter said the Irish duo of JP McManus and John Magnier, the club's biggest shareholders with a 28.9% stake, still remain crucial to any outcome.
"What will be going through Mr Glazer's head is the what he will always have been aware of - that any formal bid will fail without their agreement."