What does Spain financial issues have to do with anything here. Madrid is in debt just like United, but the club actually makes money (you know, profit at the end of the fiscal year), just like United.
So were's the difference?
I don't think you realize the difference between United, Arsenal, Madrid, Barca, Bayern on one side and Chelsea, City, PSG on the other. You see, the latter three wouldn't be able to function like they do in normal economic circumstances because no bank would loan them the money to buy these expensive players, simply because they would never be able to pay them back. That's the reason why FFP has been introduced, because those three would eventually make life impossible for the clubs like United or Madrid. They would never need to balance the books and all the other honest living clubs would pay the price for that.
Btw, do you know that even the most successful companies on fortune 500 are almost all in some kind of debt. Debt by itself is not good or bad, debt is normal. It's what enables us to live a better life and it enables the clubs we support to sign top players.....and it also makes the world go round.