I don't think you grasped what I was saying. The club's borrowings are not the issue (except they're only worth about £1.6bn at the moment not £2bn) but most of the assets, Old Trafford included, are used as security for their borrowings.
The majority of shares are held by the Glazers. The Glazers have another business called First Allied Corporation, which manages shopping malls. They own those malls and rent the units out to shops. It's like a huge buy-to-let operation where the plan is that the rental payments cover the interest on the mortgages on the malls. Just prior to the crash in 2008, they re-mortgaged these malls heavily. The security was presumably the malls so as long as they're worth more than the mortgage and the interest payments are covered, everything's fine. The crash put a stop to that however and a number were in default with some going into liquidation.
The Glazers also presumably had to borrow money to repay the PIK notes they used to finance the purchase of united. That may well have been done using their united shares as security as these seem to be the one tradeable asset they have. Also, if the mortgages on the malls are higher than the capital value of those properties, they may have been asked for additional security. Again, their united shares are an obvious source for that. If the share price goes down significantly (even after a $1 rise today they're down 20% on recent weeks) they may be asked for more security as the value of that security goes down.
The First Allied malls are at the low-end of the market, without the prestigious anchor tenants that other malls have, and the future for anything but high-end malls generally is bleak, with many shutting down. The Glazers clearly aren't making anything out of this business as they're taking £2.5m each out of united each year and one at least has sold a large block of shares. They therefore need united to be financially successful to keep the share price high as it appears to be their only liquid asset and may be propping up other the other part of their business holdings as well as personal borrowings. If the share price were to collapse, it could seriously hurt them.
I've often wondered why they haven't got rid of united, when they had the chance to get £2bn or more. I suspect that they either can't sell the shares (as they're tied up in securing other borrowings) or that the £2bn they might have got isn't even enough to cover their various liabilities.