The 20 La Liga clubs had combined debt of 3.526 billion euros in 2008/09, up from 3.49 billion the previous season, according to the new study by University of Barcelona professor Jose Maria Gay.
Revenue growth more than halved to a tepid 4 percent, from 10 percent in the 2007/08 campaign, and operating costs rose to 1.704 billion euros, outstripping income of 1.455 billion euros by 249 million, the study showed.
Only La Liga giants Real Madrid and Barcelona, the world's two richest clubs, and lowly Numancia, who were relegated, made an operating profit.
"Let's not kid ourselves, Spanish football is in a very difficult situation, like our economy," Gay wrote.
"You can't spend more than you earn. This is the fundamental rule for economic survival."
Gay suggested this would have to change if the league wanted to prevent financial meltdown and avoid turning into a "Scottish-style" competition where two teams - Celtic and Rangers - dominated the sporting and economic arenas.
"Who can win the league? The answer is obvious: Barca or Madrid. Madrid or Barca. Nobody else," Gay said.
"Maybe now is the right time to renegotiate the rules of the economic game between all the protagonists," he added.
"Barca and Madrid will have to make an effort, sacrificing today so that the league can flourish," Gay said.
"One step back, several forward. If this does not happen, the league will be in its death throes."
"This means the economic model is unsustainable and they are often forced to fall back on extraordinary revenue to wipe out their deficits," Gay wrote.
"Like the Spanish state, soccer needs to make drastic spending cuts, especially in wages," he added. "And this means that everyone has to tighten their belts."
