Juventus chairman Andrea Agnelli says the European Super League (ESL) project cannot proceed as Inter Milan and Atletico Madrid joined the six Premier League clubs in withdrawing,reports BBC.
Agnelli was one of the chief architects of the breakaway plans, which involved 12 clubs from England, Spain and Italy.
But with eight of the 12 teams pulling out, he accepts it cannot now go ahead.
"To be frank and honest no, evidently that is not the case," said Agnelli, on whether the ESL could still happen.
"I remain convinced of the beauty of that project, of the value that it would have developed to the pyramid, of the creation of the best competition in the world, but evidently no. I don't think that project is now still up and running."
Atletico Madrid and Inter Milan announced their withdrawal on Wednesday morning.
The Juventus chairman was described as a "snake and a liar" by Uefa president Aleksander Ceferin on Monday after the announcement of the breakaway plans on Sunday evening.
Agnelli resigned his position as chairman of the European Clubs' Association on Sunday and refused to take calls from Ceferin.
The six Premier League clubs involved all withdrew within hours of each other on Tuesday following a furious backlash against the plans.
Manchester City were the first club to pull out after Chelsea had signalled their intent to do so by preparing documentation to withdraw.
The other four sides - Arsenal, Liverpool, Manchester United and Tottenham - then followed suit late on Tuesday evening.
In announcing their withdrawal on Wednesday, Atletico Madrid said "harmony is essential" between the club and the fans, and added that the first-team squad and coach Diego Simeone had backed their decision because "sporting merits must prevail over any other criteria".
In their statement, Serie A side Inter Milan said they were "committed to giving fans the best football experience", adding: "Our engagement with all stakeholders to improve the football industry will never change."
The 12-team Super League, which also included Spanish sides Barcelona and Real Madrid and Italy's AC Milan and Juventus was announced on Sunday to widespread condemnation.
"Despite the announced departure of the English clubs, forced to take such decisions due to the pressure put on them, we are convinced our proposal is fully aligned with European law and regulations," the ESL said earlier on Wednesday, adding it was "convinced that the current status quo of European football needs to change".
"Real Madrid president Florentino Perez is insisting on the idea of keeping the group together to push for change," says Spanish football expert Guillem Balague.
"Barcelona say they agreed to the ESL, but only if the season ticket holders' assembly approve it, which could be their way out."