A group of 12 super clubs have officially confirmed their plans to form a breakaway Super League, despite the threat of stern action by UEFA.
The governing body of European football was due to approve Champions League reform plans at Monday's meeting of the executive committee.
But a shock move from some of the world's biggest clubs threw the plans into chaos.
The so-called 'Big Six' of the English Premier League have signed on to a plan to form a breakaway league.
A closed shop league has long been the dream of Real Madrid president Florentino Perez, and both his club and Barcelona are backing the plan.
Manchester United, Liverpool, Manchester City, Arsenal, Chelsea and Tottenham are also on board, as are Atletico Madrid, Inter and Milan.
Andrea Agnelli, head of the European Club Association, was one of the main driving forces behind the Champions League reforms which will be voted on at the executive committee meeting.
He has always insisted that he does not want a closed shop, but Agnelli's club Juventus are also backing the plan.
Announcing the move the 12 clubs said: "Twelve prestigious European clubs today jointly announce an agreement to form a new midweek football competition, the Super League, governed by the founding clubs.
"AC Milan, Arsenal FC, Atletico de Madrid, Chelsea FC, FC Barcelona, FC Internazionale Milano, Juventus FC, Liverpool FC, Manchester City, Manchester United, Real Madrid CF and Tottenham Hotspur have all joined as founding clubs.
"Three more clubs are expected to join as founding clubs before the inaugural season, which is expected to start as soon as possible.
"In the future, the founding clubs look forward to consulting with UEFA and FIFA in order to work together and cooperate to acheive the best possible outcome for the new league and for football as a whole.
"The formation of the Super League comes at a time when the global pandemic has accelerated the instability in the existing European football economic model. Further, for a number of years, the Founding Clubs have had the objective of improving the quality and intensity of existing European competitions throughout each season, and of creating a format for top clubs and players to compete on a regular basis.
"The pandemic has shown that a strategic vision and a sustainable commercial approach are required to enhance value and support for the benefit of the entire European football pyramid. In recent months extensive dialogue has taken place with football stakeholders regarding the future format of European competitions. The Founding Clubs believe the solutions proposed following these talks do not solve fundamental issues, including the need to provide higher-quality matches and additional financial resources for the overall football pyramid."
The plan is backed by US bank JP Morgan Chase, which is willing to invest around £5bn set against future television revenues.
There would be 20 participating clubs with 15 founding clubs and a qualifying mechanism for a further five teams to qualify annually based on achievements in the prior season.
Perez, who has been elected chairman of the new league, said: "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 four billion fans and our responsibility as big clubs is to respond to their desires.”
Manchester United co-chairman Joel Glazer added: "By bringing together the world’s greatest clubs and players to play each other throughout the season, the Super League will open a new chapter for European football, ensuring world-class competition and facilities, and increased financial support for the wider football pyramid.”
Broadcaster DAZN is believed to be ready to pay £3bn for the rights, with the competition to begin in 2022, but the 12 face a fight with UEFA and their own domestic leagues.
A statement signed by the European governing body, the English, Spanish and Italian FAs, as well as the Premier League, La Liga and Serie A, warned: "We will consider all measures available to us, at all levels, both judicial and sporting in order to prevent this happening. Football is based on open competitions and sporting merit; it cannot be any other way.
"As previously announced by FIFA and the six Confederations, 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.
"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."
And leading figures both inside football and out have spoken out against the plans.
UK Prime Minister Boris Johnson said: "Plans for a European Super League would be very damaging for football and we support football authorities in taking action.
"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."
And Manchester United's legendary manager Sir Alex Ferguson also slammed the plans.
He told Reuters: "Talk of a Super League is a move away from 70 years of European club football. Both as a player for a provincial team Dunfermline in the 60s and as a manager at Aberdeen winning the European Cup Winners’ Cup, for a small provincial club in Scotland it was like climbing Mount Everest.
"Everton are spending £500 million to build a new stadium with the ambition to play in Champions League. Fans all over love the competition as it is
"In my time at United, we played in four Champions League finals and they were always the most special of nights."
No French side has signed up, and the French FA also came out against the plans.
A statement said: "The FFF and the FLP oppose the whole project relating to the European Super League. Alongside UEFA, the FFF and FLP are positioned firmly against a project that threatens the entire pyramid of European football.
"The hegemonic dreams of an oligarchy will result in the disappearance of a European system that has allowed football to develop in an unprecedented way in Europe.
"By breaking this balance, the Super League project will put an end to a system based on sporting merit and which has been able to put in place mechanisms of solidarity with all the European federations."
And even the ECA, of which Agnelli was head, made clear it "supports a commitment to work with UEFA on a renewed structure for European club football".
Perhaps unsurprisingly the Juve chief resigned his position shortly after the statement as his club left the organisation.