In a programme to be screened tomorrow night, BBC's Panorama says the Glazer family's debts total more than £1.1billion - £700million tied to Manchester United, £388million on mortgages for their First Allied shopping mall business in the United States and £66million tied to their Tampa Bay Buccaneers NFL team.
The Glazers say they are comfortable with the situation and that their assets total £2billion.
But investment analyst Andy Green, who investigated the Glazers' finances for Panorama, believes the Glazers have no option but to raid United's coffers to pay off the payment in kind loans - PIKs - which total £220million.
These PIKS carry a 16.25% interest rate and unless any payments are made these loans will spiral to £600million by 2017.
Green, a United fan, said: "This is not meant to be scaremongering - the Glazers have a stark choice to pay off the PIKs or risk losing the club.
"What I care about is Manchester United being used as a piggy bank to pay off loans instead of money being invested in the team.
"That is even more important with Manchester City, Chelsea, Barcelona and Real Madrid spending money like it's going out of fashion.
"The money the Glazers make from First Allied and the Buccaneers is totally inadequate to deal with the PIKs - only Manchester United can provide the money to deal with those."
Green said the £500million United bond issue in January now allowed the Glazers to take money out of the club where as previous bank loans had not allowed them to do so.
The investigation will give impetus to the 'green and gold' campaign being run by some United fans against the Glazers' ownership.
There is also a proposed takeover by a group of wealthy United fans known as the Red Knights, though no bid has materialised and the Glazers insist they have no intention of selling the club.
In March, United chief executive David Gill insisted the club's debts were easily covered by the income.
He said then: "We have an element of the debt that is very easily serviced by the cashflows of Manchester United, we are in a sport that is getting bigger all the time and as one of the leading clubs we should benefit from that growth.
"We believe we have a much more appropriate and flexible financial structure in place.
"In an ideal world people would like to not have a mortgage on their house but that doesn't mean they don't enjoy the benefits of living in that house and can't afford that house."
He also insisted the £80million transfer fee from the sale of Cristiano Ronaldo was still available for manager Sir Alex Ferguson to spend on top players.
A spokesman for the Glazer family was unavailable for comment.