La Liga chief Javier Tebas has called plans for a European Super League "weak and imaginary" and declared it would bring ruin to clubs.
Outgoing Barcelona president Josep Maria Bartomeu used his final press conference to announce that the Catalan giants have signed up to the so-called European Premier League plan.
The move, believed to be supported by Liverpool and Manchester United, would see 16 or 18 teams compete in a re-imagined Champions League.
A €5billion funding package expected to be put in place, with Juventus also likely to support the move that has long been touted by president and European Club Association chair Andrea Agnelli.
They'll face resistance from UEFA and domestic leagues though, with La Liga's president firing an immediate rebuke.
Tebas wrote on Twitter: "Unfortunate Josep Bartomeu statement on his last day about Barcelona joining a weak and imaginary competition which would be their ruin.
"It confirms his ignorance about the football industry.
"A sad end for a president with successes and lately many mistakes."
Earlier on Tuesday Bartomeu revealed he had signed up to the scheme.
The departing president said: "I can announce some extraordinary news.
"Yesterday (Monday) he board of directors approved the requirements to participate in a future European Super League, a project promoted by the big clubs in Europe which will guarantee the future financial sustainability of the club.
"We can say with pride that we are the highest valued club in the world. We have achieved that ahead of clubs owned by States and billionaires, all while keeping the club in the hands of the members.
"And the European Super League guarantees the club will remain in the members' hands."
