UEFA and FIFA have reacted furiously to a move from 12 European clubs to launch "The Super League" - a new competition outside of the existing football framework which would not respect traditional promotion-relegation models - and pledged to do everything in their power to stop it.
FIFA wished to "express its disapproval" at the proposal and UEFA warned before an official announcement was made that it would "consider all measures available to us, at all levels, both judicial and sporting in order to prevent this happening".
Juventus chairman Andrea Agnelli is widely seen as a driving force behind the breakaway competition and has tonight resigned from the UEFA Executive Committee.
Juventus are among the 12 "Founding Clubs" of the new 20-team competition that would play it in every season, with an official statement saying three more are expected to join.
Two more Italian clubs, AC Milan and Inter Milan, six English teams - Manchester United, Manchester City, Liverpool, Chelsea, Tottenham Hotspur and Arsenal - plus Spanish trio Barcelona, Real Madrid and Atletico Madrid - have signed up to the rebel competition.
After The Times reported an announcement was imminent earlier today, UEFA hit out and underlined a previous pledge from FIFA, itself and football's five other continental governing bodies to ban any players who took part in a so-called European Super League from FIFA-sanctioned competitions.
The English Football Association, Royal Spanish Football Federation, Italian Football Federation and top leagues in the respective countries joined UEFA in the last-ditch attempt to stave off the new competition.
"We will remain united in our efforts to stop this cynical project, a project that is founded on the self-interest of a few clubs at a time when society needs solidarity more than ever," read a joint statement.
"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."
"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."
Real Madrid President Florentino Pérez is the first chairman of The Super League, with Agnelli and Manchester United co-chairman Joel Glazer named vice-chairmen.
FIFA has condemned the breakaway, but left wiggle room in a statement which called for "calm, constructive and balanced dialogue for the good of the game" and focused on unity.
"FIFA wishes to clarify that it stands firm in favour of solidarity in football and an equitable redistribution model which can help develop football as a sport, particularly at global level, since the development of global football is the primary mission of FIFA," said world football's governing body.
"In our view, and in accordance with our statutes, any football competition, whether national, regional or global, should always reflect the core principles of solidarity, inclusivity, integrity and equitable financial redistribution.
"Moreover, the governing bodies of football should employ all lawful, sporting and diplomatic means to ensure this remains the case.
"Against this background, FIFA can only express its disapproval to a 'closed European breakaway league' outside of the international football structures and not respecting the aforementioned principles.
"FIFA always stands for unity in world football and calls on all parties involved in heated discussions to engage in calm, constructive and balanced dialogue for the good of the game and in the spirit of solidarity and fair play.
"FIFA will, of course, do whatever is necessary to contribute to a harmonised way forward in the overall interests of football."
Proponents of The Super League - "intended to commence as soon as practicable" - will claim it is not closed, with "a qualifying mechanism" promised to offer five berths per season.
The split is one of the most consequential in modern football history, and comes on the eve of a UEFA Executive Committee meeting tomorrow where a new-look and expanded Champions League, featuring 36 teams, is expected to be approved.
Preparations for this year's European Championship were also due to be discussed, with Bilbao, Dublin and Munich given an extended deadline to inform UEFA of crowd limits for the tournament, but will doubtless be overshadowed.
Euro 2020 could now serve as a flashpoint if UEFA goes through with its threat to exclude players of rebel clubs from its competitions, although legal battles are likely to occur beforehand.