The Premier League has hit out at plans to create a European Super League, branding them anti-competitive and suggesting they undermine the integrity of the sport.
It has been joined by UEFA in slamming the proposal, which they say threatens the very structure of the game.
Previously, UEFA's Swiss model for the Champions League had been expected to be ratified at a meeting on Monday, before reports of a rival competition emerged on Sunday.
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What has been said?
In a statement, the English top-flight said: "The Premier League condemns any proposal that attacks the principles of open competition and sporting merit which are at the heart of the domestic and European football pyramid.
"Fans of any club in England and across Europe can currently dream that their team may climb to the top and play against the best. We believe that the concept of a European Super League would destroy this dream.
"The Premier League is proud to run a competitive and compelling football competition that has made it the most widely watched league in the world. Our success has enabled us to make an unrivalled financial contribution to the domestic football pyramid.
"A European Super League will undermine the appeal of the whole game, and have a deeply damaging impact on the immediate and future prospects of the Premier League and its member clubs, and all those in football who rely on our funding and solidarity to prosper.
"We will work with fans, The FA, EFL, PFA and LMA, as well as other stakeholders, at home and abroad, to defend the integrity and future prospects of English football in the best interests of the game."
What has UEFA's response been?
UEFA has also condemned the plans.
In a statement, it said: "UEFA, the English Football Association and the Premier League, the Royal Spanish Football Federation (RFEF) and La Liga, and the Italian Football Federation (FIGC) and Serie A have learned that a few English, Spanish and Italian clubs may be planning to announce their creation of a closed, so-called Super League.
"If this were to happen, we wish to reiterate that we – UEFA, the English FA, RFEF, FIGC, the Premier League, La Liga, Serie A, but also FIFA and all our member associations - 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.
"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 Federations, 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."
What have been the other responses?
They said: "It is clear that this would be damaging to English and European football at all levels and will attack the principles of open competition and sporting merit which are fundamental to competitive sport.
"For new competitions to be formed involving clubs from different assocations, approval would be required. We would not provide permission to any competition that would be damaging to English football, and will take any legal and/or regulatory action necessary."
There have been no official comments from any clubs so far. Arsenal manager Mikel Arteta refused to be drawn on the subject in his pos-match press conference after their 1-1 draw with Fulham in the Premier League on Sunday.
Arteta said: "I don’t know. Once I know every detail and I have all the information, then I can evaluate and give you an opinion."
According to a report from the Sunday Times, a breakaway group of clubs wish to create a standalone European Super League that would act in competition to the Champions League.
Reports from France added that these clubs came from England, Italy and Spain, with French and German outfits refusing to agree to the deal. These appear to have been verified by UEFA's statement.
Nevertheless, UEFA plans to put forward its proposal for a 'Swiss Model' Champions League to the ECA (European Club Association) on Monday, at which point the face of European football could be forever altered if not approved.