Spain's domestic league would suffer a 50 per cent reduction in all revenues if a "semi-closed" Super League became a reality, according to a new report by professional services firm KPMG for La Liga.
The report estimated the league's value - comprised of broadcast rights, sponsorship, season tickets and other ticketing - at 3.316 billion euros (£2.85bn) in the current season.
The existence of a Super League played in midweek would slash that value by 1.662 billion euro (£1.4bn) while if LaLiga was forced to become a midweek competition the impact is forecast to be even greater - with a reduction of 1.8billion euro (£1.5bn) - a drop of 55 per cent.
The presidents of Real and Barca, Florentino Perez and Joan Laporta, remain advocates of a Super League despite the swift collapse of the last attempt to set up such a competition in April last year.
The KPMG report states those clubs would see an uplift in revenues by 400m euros each per season, but La Liga president Javier Tebas warned any benefits would be fleeting compared to the catastrophe they would inflict on the domestic game.
"In the medium term they would lose," Tebas said via an interpreter at a press conference in Madrid to present the report.
"They're earning more but the domestic leagues will lose (revenue) and continue losing, so (Real and Barca) will be losing revenue in the domestic league.
"It might work for the first three years as far as broadcasting rights, but after the third or fourth year the value of their broadcasting rights will really drop and once they realise that it's going to fall, we will all be bankrupt.
"Madrid and Barcelona have been competing in the league for 90 years. They became big by competing in these competitions. So now, trying to kick the rest (of the clubs) in the a**, I don't think that's fair either.
"They are part of this growth because the competition has allowed them to become big clubs."
UEFA and a wide range of other representative groups met with the leaders of A22, one of the companies supporting the Super League, in Switzerland last month.
European football's governing body said A22 refused to define its new approach at the meeting, but Tebas is convinced it is looking at a "semi-closed" competition where only four of the 20 teams involved would alter each season.
The Super League case was heard at the European Court of Justice in the summer, with its supporters arguing UEFA and FIFA abused a dominant position under EU competition law by blocking the league's formation and by attempting to sanction those involved.
The opinion of the Advocate General in the case, which will be non-binding, is set to be published on December 15.
While Tebas was talking, A22 released quotes on its official Twitter account from Fernando Irurzun, the Spanish head of litigation and dispute resolution at global law firm Clifford Chance.
Irurzun said: "UEFA's mantra is to say that football is different and for this it claims to base itself on article 165 of the EU Treaty. The article does not speak of the 'European model' nor of 'allowed exceptions'.
"The Tour de France is organised by a private company. Does anyone dare to say that the Tour goes against the European model of sport?
"The EU Treaty does not say that UEFA is the only body responsible for organising football club competitions in Europe. This is the essential question that must be answered."