Atletico Madrid and Inter Milan have followed Manchester City, Chelsea, Liverpool, Arsenal, Tottenham Hotspur and Manchester United in announcing their withdrawal from the proposed European Super League (ESL).
Meanwhile, AC Milan and Juventus released independent statements later on Wednesday clarifying that the ESL can now not go forward, but stopping short of confirming they had abandoned the project altogether.
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On Sunday, 12 leading European sides confirmed the creation of a midweek breakaway tournament, with Real Madrid, Barcelona, Juventus and Milan the other teams involved.
However, following intense fan backlash, the six English clubs gradually announced they would be withdrawing on Tuesday, before Atletico and Inter followed suit on Wednesday.
"Atletico Madrid's administrative council met on Wednesday morning and has decided to formally communicate to the Super League and the rest of the founding members our decision to no longer form a part of the project," an Atletico statement read.
"Atletico Madrid took the decision to withdraw from the project on Monday in response to circumstances which mean it is no longer possible. For the club, it is essential that all members of the Rojiblanco family were in harmony, especially our fans."
Sources told ESPN that Atletico had initially viewed the proposals favourably and had not expected the "rejection" of the decision from fans and supporter groups.
"The first-team squad and the manager have shown their satisfaction with the club's decision, understanding that sporting merit should be above any other criteria," the statement added.
Sources had also told ESPN that the squad's unhappiness with the club's involvement had also played a part in the decision, and later on Wednesday, Atletico captain Koke released a statement on behalf of himself and his teammates confirming this.
"We want to express our satisfaction at the final decision taken by the club to withdraw from the Super League project," it read. "We will keep fighting from our position to help Atleti grow through the values of effort and sporting merit that have always characterised us."
Speaking in a news conference ahead of Atletico's clash with Huesca shortly after Atletico's announcement, manager Diego Simeone said: "I believed that the club would do what it thought was best for the club.
"We think it's good to look to our fans, and above all to look to the Atletico family, the staff, players, the president, everyone around Atletico Madrid.
"What I think, I say it to the people I have to say it to. And I tell them what I feel. I don't want to say more here ... I trusted the club. We think this is good for everyone."
Sources had told ESPN on Tuesday that Inter were planning to withdraw from the Super League and they made their decision official on Wednesday.
"FC Internazionale Milano confirm that the club is no longer part of the Super League project," an Inter statement read.
"We are always committed to giving fans the best football experience; innovation and inclusion are part of our DNA since our foundation. Our engagement with all stakeholders to improve the football industry will never change.
"Inter believes that football, like every sector of activity, must have an interest in constantly improving its competitions, to keep on exciting fans of all ages around the world, within a framework of financial sustainability.
"With this vision we look forward to carry on working together with institutions and all stakeholders for the future of the sport we all love."
Barca also distanced themselves from the project on Tuesday, confirming that participation would be conditional on La Liga club's members voting in favour of the proposal, sources told ESPN.
Prior to the announcements made by Atletico and Inter, Juve president Andrea Agnelli had said he felt the decisions taken by the English sides to withdraw had meant the Super League "cannot go ahead."
Later on Wednesday, Milan also released a statement explaining their position with regards to the Super League. It read: "We accepted the invitation to participate in the Super League project with the genuine intention to deliver the best possible European competition for football fans around the world and in the best interest of the club and our own fans.
"Change is not always easy, but evolution is necessary for progress, and the structures of European football have evolved and changed over the decades.
"However, 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. We will continue to work hard to deliver a sustainable model for football."
Juventus followed suit shortly after, with a statement that read: "With reference to the press release published by Juventus Football Club S.p.A. on 19 April 2021, relating to the proposed creation of the Super League, and the ensuing public debate, the issuer clarifies to be aware of the request and intentions otherwise expressed by certain clubs to withdraw from this project, although the necessary procedures envisaged by the agreement among the clubs have not been completed.
"In this context, 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.
"Juventus remains committed to pursuing the creation of long-term value for the Company and the entire football industry."
Sunday's announcement of the league's creation to replace the Champions League had sent shock waves through the football world and beyond.
In a TV interview on Monday night, Madrid president Florentino Perez -- named the Super League's first chairman -- cited reduced revenues and waning interest from young people in football as the primary motivations for the project, saying "we want to save football" and clubs "will all die" without such major reform.
However, pressure from football's governing bodies, politicians and fans -- especially in the United Kingdom -- forced the six Premier League clubs involved to withdraw on Tuesday night.