The two Milan giants and Atletico Madrid followed all six English Premier League clubs in pulling out of the European Super League on Thursday, dealing a fatal blow to the project as besieged owners launched damage-limitation exercises, desperate to head off sanctions.
The withdrawals by Manchester City, Manchester United, Liverpool, Arsenal, Chelsea and Tottenham came just 48 hours after the league's unveiling on Monday following a furious response from fans and officials.
The three Italian clubs involved — Juventus, AC Milan and Inter Milan — admitted defeat and La Liga leaders Atletico Madrid also pulled out.
Real Madrid and Barcelona — the last of the initial group of 12 clubs to sign up — have yet to make any comment on their future plans but the project in its current form is dead in the water.
Man Utd, Liverpool try to back track
Some of the key players in the bungled breakaway are now issuing grovelling apologies.
"We got it wrong," said Manchester United co-chairman Joel Glazer in his first public comments since the tournament was announced.
"This is the world's greatest football club and we apologise unreservedly for the unrest caused during these past few days."
Glazer's apology followed an earlier similar act of contrition by Liverpool owner John W Henry.
The American also apologised and added: "It goes without saying but should be said, the project put forward was never going to stand without the support of the fans … Our work isn't done. And I hope you'll understand that even when we make mistakes, we're trying to work in your club's best interests. In this endeavour I've let you down."
Henry's apology rang hollow with some. "(He's) still trying to claim that his aims were altruistic. Still insisting he cares about the fans despite never once considering consulting them on his carve-up. That can't be forgotten or forgiven. He, and others, must be forced to cede ground or forced out," UK journalist Daniel Storey said.
"He tried to copyright the word Liverpool. Tried to furlough staff. Tried to force through Project Big Picture. Tried to charge fans £77 for tickets. Tried to break away to a Super League. An apology only carries weight if it suggests you have learnt from your mistakes. How many?"
UEFA ponders punishments: 'They will live with shame'
However, the climbdowns may not save the 12 clubs from punishment.
Many rival clubs want sanctions handed down and UEFA vice president Karl-Erik Nilsson said its executive committee would decide whether to take action at its next meeting on Friday.
"We will have to discuss possible additional consequences, the first consequence is that they will live with shame," Nilsson said.
AC Milan were one of the main drivers behind the plans, having missed out on the riches of the Champions League for the past seven seasons.
The seven-time European champions said a shake-up was necessary due to the changing football landscape but admitted they "must be sensitive to the voice of those who love this wonderful sport".
Italian champions Juventus said they remained "convinced of the soundness of the project's sport, commercial and legal premises" but accepted it could not go ahead in its original form.
Why it happened in the first place
The Super League promised guaranteed entry for its founding clubs and billions of dollars in payments.
Many of the clubs have huge debts and wage bills, and suffered a sharp drop in revenues during the coronavirus pandemic.
But the project was vehemently opposed across the football spectrum, from fans to players, coaches, politicians, UEFA and FIFA.
The clubs were threatened with a ban from domestic and European football, while their players could even have been barred from representing their countries.
UEFA president Aleksander Ceferin had struck a conciliatory tone on Wednesday, saying he wanted to "rebuild the unity" of European football, and described the English clubs as "back in the fold".
"I said yesterday that it is admirable to admit a mistake and these clubs made a big mistake," Ceferin said in a statement.
"The important thing now is that we move on, rebuild the unity that the game enjoyed before this and move forward together."
Shares in Juventus plunged by more than 13 per cent on Wednesday following a slump in the value of Manchester United stocks on Tuesday.
In response to the English pull-outs, the Super League had said it was looking for ways to "reshape", insisting the "status quo of European football needs to change".
"We shall reconsider the most appropriate steps to reshape the project," its statement said.
British Prime Minister Boris Johnson hailed the English pull-outs, telling parliament: "The announcement was the right result for football fans, for clubs and for communities across the country." Reigning European champions Bayern Munich and French giants Paris Saint-Germain had both come out strongly opposed to the breakaway league, dealing it a heavy blow.
Adding to the drama on Tuesday, Manchester United announced that executive vice-chairman Ed Woodward would step down from his role at the end of 2021.
Several players at the English clubs had voiced opposition to the Super League, and Manchester City manager Pep Guardiola commented: "It's not a sport when success is already guaranteed."