The Red Knights, made up of wealthy United fans, has recruited the Japanese investment bank Nomura to help it put together a bid which will interest the Glazers, who for their part have said United are not for sale.
But the group, which includes Jim O'Neill, chief economist at Goldman Sachs, lawyer Mark Rawlinson and financier Keith Harris, says the number of fans willing to invest in a takeover bid is growing.
Their statement added: "The Red Knights have been liaising with the Manchester United Supporters Trust, and their representatives were at our first meeting on 2 March. They remain closely involved with our plans.
"On 12 March we involved Nomura as our adviser. Since then they have been speaking to and meeting many potential Red Knights who have contacted us since our interest was made public.
"These potential Red Knights have offered ideas and support and, with the help of this input, our plans have been developed further."
The Glazers, meanwhile, have insisted that the club is not for sale and manager Sir Alex Ferguson has been publicly supportive of the Americans.
But the 'Green and Gold campaign' has seen thousands of supporters wear the colours of United under their original guise of Newton Heath, with former United hero David Beckham donning a scarf after AC Milan's Champions League defeat at Old Trafford.
The Red Knights believe they will need to raise between £800m and £1bn to launch a serious bid for the club.
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