Superphil
Dismember
There was a good analysis of this done a couple of years ago by swissramble. When the debts were compared like-for-like both Barcelona and Real Madrid had an almost identical level of debt to Arsenal (around £100m each). Manchester United's debt was four times that.
The report I read this morning differed to that, as indeed do most reports, perhaps things have changed in the last couple of years. Seeing as Barcelona are owned by the fans, it makes you wonder how they are allowed to run up any debt, let alone hundreds of millions. United are owned by a business, who manage their debt, and who have securities against the debt.