Barcelona joined Real Madrid in clinging desperately to the wreckage of their doomed Super League project on Thursday as the breakaway tournament’s 12 founders faced mounting calls for reprisals.

European governing body Uefa will meet on Friday where they could opt for punishment or peace with the clubs who were forced into an embarrassing climbdown that saw their plan, condemned as a greed-induced landgrab, implode inside 48 hours.

“There will be consequences in their own organisations, and whether there will be further consequences is something we need to discuss,” said Uefa vice-president Karl-Erik Nilsson.

On Thursday only Real, Barca and Juventus had yet to officially concede defeat.

Manchester City, Manchester United, Arsenal, Liverpool, Tottenham Hotspur and Chelsea withdrew on Tuesday, followed by Atletico Madrid, Inter Milan and AC Milan 24 hours later.

Juve admitted the project could not proceed.

From English U-turn to reluctant bow by the Italians: How the Super League project collapsed

However, Barcelona said it would have been an “historical error” to turn down the chance to join the Super League, with the club deciding to remain part of the project for now.

In an unapologetic statement, Barca said it would carry out an “in-depth analysis” of the breakaway competition before putting the final decision to a vote among the club’s members.

Barca president Joan Laporta described the Super League as a “necessity”.

Super League chief Florentino Perez, president of Real Madrid, had was adamant late Wednesday the rebel competition was merely “on standby”.

Uefa president Aleksander Ceferin said although he wanted to “rebuild the unity” he did not rule out some form of payback.

“I can’t go into details, we are discussing it with our legal department,” he said ahead of Friday’s meeting.

Uefa member, Javier Tebas, the president of the Spain’s La Liga, urged restraint.

“Everyone wants to cut everyone’s head off,” he said. “We have procedures. We don’t need to rush into things.”

Meanwhile, Manchester United fans breached security at their club’s training ground on as they protested against the Glazer family for the owners’ role in the failed league. United manager Ole Gunnar Solskjaer was forced to speak to around 20 supporters after they blocked both entrances to the Carrington headquarters.

‘We decide when you play’

The protestors unfurled banners that read “51% MUFC 20”, “We decide when you play” and “Glazer out”.

The 51% is a reference to fans holding the majority of voting rights at a club, which is commonplace in German football. Bayern Munich came out strongly opposed to the Super League.

Supporter groups are calling for “real change” at their clubs, whose foreign owners are often seen as aloof and out of touch with fans.

“The Super League is dead. Now we need to work with government to change how English football clubs are owned,” said the Arsenal Supporters’ Trust, while the Spirit of Shankly group accused Liverpool owner John Henry of “crocodile tears” in his apology.

“This debacle must be a catalyst for real change, not an exercise in damage limitation,” the fan group said.

Arsenal boss Mikel Arteta said he had received a personal apology from club owner Stan Kroenke and saluted supporters for sending the “strongest message” football has ever seen.

Arteta believes the rapid and passionate response fans of Premier League clubs played a key role in convincing the owners to back down in their Super League plans.

“This has given big lessons and it shows the importance of football in the world,” Arteta said. “It shows that the soul of this sport belongs to the fans.”

Manchester City boss Pep Guardiola called the controversy a “closed chapter” following his side’s 2-1 victory at Aston Villa.

Three of the rebel clubs are involved in the Champions League semi-finals next week.

Premier League leaders Manchester City are due to play Paris Saint-Germain, conspicuous by their absence from the Super League plans, on April 28, a tie Ceferin expects to go ahead as scheduled.

Record 13-time winners Real Madrid face Chelsea in the other last-four clash.

“There is relatively little chance that next week’s matches will not be played,” Ceferin told Slovenian television channel Pop TV.