Just as Spain's economic crisis has been largely fueled by banks lending large sums of money to fuel a speculative property bubble and unneeded infrastructure (not to mention a healthy dollop of unsustainable feeding at the public trough by many regional politicians and their friends), so La Liga's success has been fueled by unsustainable borrowing--from other clubs, from the taxman, from banks.
As he states, "football continues to be a true reflection of the economy", and, one is tempted to note, of economic management. Not surprisingly, he feels the best league in Europe is the Bundesliga: stadiums are full, matches are exciting, the league is very competitive and all the clubs share relatively equally in broadcast revenues.
Interestingly, he is less sanguine about the EPL, noting that as a whole its clubs, like those in the Italian and Spanish leagues, are technically insolvent. Success (Manchester City, Chelsea, Manchester United) is being achieved by higher and higher levels of debt or personal investment that will never be recouped, which is not sustainable in the long-term either, especially not if UEFA's Financial Fair Play regulations actually have some teeth to them.
As for Spain, Professor Gay says "the league is dying" and gives Spanish football "less than five years" to survive unless major changes take place. Only Barcelona and Real Madrid are growing; the rest are standing still at best. It's a familiar story now, but when two clubs each have four times as many TV revenues as the next highest club, it's difficult to compete. (even more difficult when commercial and matchday revenues are even more unequal).
Clubs have spent well beyond their means on quality players, and this can't continue--especially since tax changes now mean the advantage Spanish clubs enjoyed in signing overseas stars (the "Beckham rule") is now gone. Spanish clubs apart from Barca/Madrid will continue to cash in on their domestic talent--as has happened with Torres, Mata, Cazorla, etc. (hence the photo). Teams will need to rely more on their network of scouts, and their youth systems, to succeed.
Although Professor Gay doesn't speak directly about specific clubs, it's easy to see, looking around La Liga, plenty of examples of clubs that are struggling compared to a year or two ago. The need to balance the books is being emphasized by everyone--Bilbao used its Javi Martinez windfall to pay down debt, not invest in the squad; Espanyol came out during the summer and announced they would be net sellers; everyone expects Falcao to leave Atleti in the transfer window; Valencia's stadium project has fallen apart again and they have said they'll be selling more players--the list goes on.
Of course, Villarreal found out last year that the margin for error is very small when you're trying to remain fiscally prudent yet competitive on the pitch. And let's not kid ourselves--the Submarine benefited through the years from the 'loose money' floating around, just as all clubs did. The shirt sponsorships with Castellon Airport and the Valencian Community were the most obvious examples, and those have both gone.
The success of Barcelona and Real Madrid in Europe does mean it's not likely La Liga will lose its fourth CL place, and Spanish clubs have generally been successful in making it through the last qualifying round. And, as we saw last year with Villarreal, even abject failure in the group stage still brings some decent financial return. So a couple of clubs a year can get €10-20m in revenues from UEFA, which is a nice chunk of change when you're operating on a €30-50m budget as so many clubs are.
But at some point (and we may be reaching it) the gap in revenues between Barcelona and Real Madrid and the rest will become so great that the big two may go their own way, being absorbed into some sort of European "super league", an idea which has been tossed around, or some morphed Champions League. If that happens, where will that leave La Liga?