Atlético Madrid, Inter Milan, AC Milan and Juventus all dropped out of the Super League on Wednesday, leaving the new competition essentially extinct before it even started.
Only Spanish clubs Real Madrid and Barcelona are still officially involved.
The moves by Atlético, Inter, AC Milan and Juventus came a day after the six Premier League clubs involved in the project gave up on the controversial breakaway competition.
English clubs Arsenal, Chelsea, Liverpool, Manchester United, Manchester City and Tottenham deserted the plans for the largely-closed competition amid an escalating backlash from their supporters and warnings from the government that legislation could be introduced to thwart them.
The Super League project was overseen by Real Madrid president Florentino Pérez, who promoted it as a way to "save soccer" and the clubs struggling financially amid the coronavirus pandemic.
UEFA threatened to ban players from the participating teams from playing in this year's European Championship and next year's World Cup. But a Madrid court later issued a preliminary ruling stopping UEFA, FIFA and its members from acting against the creation of the new league.
AC Milan signaled it was leaving a few hours after Atlético and Inter Milan made their announcements.
"The voices and the concerns of fans around the world have clearly been expressed about the Super League, and AC Milan must be sensitive to the voice of those who love this wonderful sport," the Italian club said.
Juventus followed moments later, but didn't completely abandon plans for a future Super League.
"While Juventus remains convinced of the soundness of the project's sport, commercial and legal premises, it believes that at present there are limited chances that the project be completed in the form originally conceived," the club said. "Juventus remains committed to pursuing the creation of long-term value for the Company and the entire football industry."
Atlético said the decision was made after its board of directors met on Wednesday.
The Spanish club said it "decided to formally communicate the Super League and the rest of the founding clubs its decision not to formalize its participation in the project."
Atlético said the "circumstances" that allowed it to join the new league on Monday "no longer existed today."
"For the club, harmony is essential for everyone involved in the (Atlético) family, especially our fans," it said. "The first team squad and its coach showed satisfaction with the club's decision, understanding that sporting merits must prevail over any other criteria."
Inter said the club was committed to delivering the best soccer experience for fans because "innovation and inclusion have been part of our DNA since our foundation."
"Our commitment with all stakeholders to improve the football industry will never change," the Italian club said. "Inter believe that football, like any sector of activity, must have an interest in constantly improving its competitions in order to continue to excite fans of all ages all over the world, within a framework of financial sustainability."
