A group of financiers - dubbed the "Red Knights" - has met to discuss a billion-pound takeover of Manchester United, BBC Sport understands.United are owned by the Glazer family, but the club's high level of debt - now at £716.5m - has prompted much unease. [LNB]Goldman Sachs economist Jim O'Neill, who was acting in a personal capacity, lawyer Mark Rawlinson and financier Keith Harris were at the meeting. [LNB]A spokesman for the Glazers told BBC Sport: "United is not for sale." [LNB]However, United's owners are now facing a two-pronged attack over their control of the club with the Manchester United Supporters' Trust (Must) running a vocal campaign to bring about a change of ownership.[LNB] [LNB][LNB]Keith Harris reveals interest in Man Utd takeover[LNB]Must's chief executive Duncan Drasdo confirmed the group had been in attendance at Monday's Red Knight meeting and had been involved in discussions with the group "for some time". [LNB]"This development is hugely welcome as there is a genuine desire to see a change of ownership at Manchester United," he said. [LNB]"Initially the Red Knight Group has effectively set a challenge to Manchester United supporters to demonstrate they wish to see an alternative ownership proposal developed. [LNB]"In the first instance supporters are being asked to do this simply by joining the free online membership of the Supporters Trust and swelling its ranks to an initial target of at least 100,000. [LNB]"It is also essential for a majority of two key groups, the Old Trafford Season Ticket holders and those with Executive facilities, to show their appetite for participation by joining the Must online campaign." [LNB]Must has recruited 53,520 members and recently started working with Blue State Digital, a communications agency that worked on Barack Obama's successful US Presidential election campaign. [LNB]Their "Green and Gold" campaign has seen supporters don the colours of Newton Heath - the club was renamed Manchester United in 1902 - with plenty of green and gold scarves in evidence at Sunday's Carling Cup final. [LNB]BBC sports news correspondent Gordon Farquhar says the idea of an attempt to oust the Glazers has been a long time in coming. [LNB]"The takeover of Manchester United by the Glazers was controversial, and many fans were opposed to the way the deal was put together, involving high levels of borrowing," he said. [LNB]"The latest accounts show debts at United's parent company increased to more than £700m, and a recent bond issue, while successful, raised concerns further [LNB]"The vocal campaign has been stiffened by the emergence of the Red Knights group which includes bankers and business experts. [LNB]"Keith Harris has advocated fans starving the club of cash by not renewing season ticket or buying merchandise to force the club to consider a sale [LNB]"Should that happen this consortium wants to be ready to make an offer but for now, according to the Glazers' spokesman, the door is firmly closed." [LNB]The City financiers insist that their initiative is about changing the owners and that they have complete confidence in chief executive David Gill and manager Sir Alex Ferguson. [LNB]The "Red Knights" group also accepts that any takeover would have to be agreed by the Glazers, but that the club's American owners cannot prevent them from putting forward a proposal.[LNB]Man Utd fans have staged 'green and gold' protests against the GlazersThe financiers are also understood to want supporters to play a key role in their campaign. [LNB]According to the latest accounts that were released in January, debts at United's parent company Red Football Joint Venture have increased to £716.5m. [LNB]Red Football Joint Venture is owned by the Glazer family and secures its debts against the football club, but the accounts also confirmed that six of Malcolm Glazer's children were each given loans worth £1.67m from the parent company.[LNB] The green and Gold campaign has really had a BIG impact, it's got them worried, but it was never meant to get rid of them Stretford_Ender85 All are directors of Red Football, and such a practice is legal, but Harris, who is the head of merchant bank Seymour Pierce, has said it did "not create a good impression of the directors' governance of the company". [LNB]On Sunday, United beat Aston Villa 2-1 in the Carling Cup final to give Ferguson his 34th trophy with the club. [LNB]The "Red Knights" group is due to release a statement on Tuesday.