Twelve of Europe's top football clubs launched a breakaway Super League on Sunday, in what is certain to be a bitter battle for control of the game and its lucrative revenue.
The move sets up a rival to UEFA's established Champions League competition and was condemned by football authorities and political leaders.
Manchester United, Real Madrid and Juventus are among the leading members of the new league, but UEFA has threatened to ban them from domestic and international competition and vowed to fight the move.
French President Emmanuel Macron and British Prime Minister Boris Johnson both issued statements condemning the breakaway and supporting UEFA's position.
Along with United, English Premier League clubs Liverpool, Manchester City, Chelsea, Arsenal and Tottenham Hotspur have signed up to the plans.
Barcelona and Atletico Madrid from Spain join Real. AC Milan and Inter Milan make up the trio from Italy along with Juventus.
The Super League said they aimed to have 15 founding members and a 20-team league with five other clubs qualifying each season.
The clubs would share a fund of 3.5 billion euros ($4.19 billion) to spend on infrastructure projects and to deal with the impact of the COVID-19 pandemic.
"We will help football at every level and take it to its rightful place in the world. Football is the only global sport in the world with more than 4 billion fans and our responsibility as big clubs is to respond to their desires," said Real Madrid president Florentino Perez, the first chairman of the Super League.
No German or French clubs have yet to be associated with the breakaway.
World soccer's governing body, FIFA, expressed its "disapproval to a 'closed European breakaway league' outside of the international football structures."
But there was no mention of a previous threat from FIFA to ban any players taking part in a breakaway from participating in World Cups.
The announcement came just hours before UEFA is to sign off on its own plans for an expanded and restructured 36 team Champions League on Monday.
UEFA issued a strong statement jointly with English, Spanish and Italian leagues and football federations, saying they were ready to use "all measures" to confront any breakaway and saying any participating clubs would be banned from domestic leagues, such as the Premier League.
"The clubs concerned will be banned from playing in any other competition at domestic, European or world level, and their players could be denied the opportunity to represent their national teams," UEFA said.
"We thank those clubs in other countries, especially the French and German clubs, who have refused to sign up to this. We call on all lovers of football, supporters and politicians, to join us in fighting against such a project if it were to be announced. This persistent self-interest of a few has been going on for too long. Enough is enough."
The moves were condemned by football authorities across Europe and former players such as Manchester United's ex-captain Gary Neville who called it "an absolute disgrace" and said the club owners were motivated by "pure greed."
France’s Macron raised his voice against the breakaway.
"The president of the republic welcomes the position of French clubs to refuse to participate to a European football Super League project that threatens the principle of solidarity and sporting merit," the French presidency said in a statement sent to Reuters.
"The French state will support all the steps taken by the LFP, FFF, UEFA and FIFA to protect the integrity of federal competitions, whether national or European," the Elysee added, citing the national, European and globally soccer governing bodies.
Britain’s Johnson also opposed the move.
"Plans for a European Super League would be very damaging for football and we support football authorities in taking action," he tweeted.
"They would strike at the heart of the domestic game and will concern fans across the country. The clubs involved must answer to their fans and the wider footballing community before taking any further steps."
There have been reports of a breakaway for several years and they returned in January with several media reported a document had been produced outlining the plans.
In October, then Barcelona president Josep Maria Bartomeu said the club had accepted a proposal to join a breakaway league.
Those reports led FIFA and UEFA to warn that they would ban any players involved in a breakaway from playing in the World Cup or European Championship.