UEFA president Aleksander Ceferin insisted players who represent clubs competing in the European Super League will be banned from international competitions despite pre-emptive legal moves by the new organisation.
Six Premier League sides – Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham – are part of an initial group of 12 clubs seeking to establish a new 20-team continental competition "as soon as practicable".
If the plans succeed it would devastate existing European club competitions and in particular the Champions League. A joint statement including UEFA and the English, Italian and Spanish leagues on Sunday said it would consider "all measures, both judicial and sporting" to prevent the competition going ahead.
On Monday, Ceferin said: "UEFA and the footballing world stand united against the disgraceful self-serving proposal we have seen in the last 24 hours from a select few clubs in Europe that are fuelled purely by greed.
"The players who will play in the teams that might be playing in the closed league will be banned from playing the World Cup, and so they will not be able to represent the national teams at any matches.
"In my opinion, this idea is a spit in the face of all football lovers, and our society as well. So we will not allow them to take it away from us."
World governing body FIFA has called for "calm, constructive dialogue" to resolve the crisis, but the company behind the Super League has taken steps to protect itself against any legal challenges.
In a letter to UEFA and FIFA, seen by the PA news agency, the Super League wrote: "We are concerned that FIFA and UEFA may respond to this invitation letter by seeking to take punitive measures to exclude any participating club or player from their respective competitions.
"We hope that is not your response to this letter and that, like us, your organisations will recognise the immediate benefits of the competition established by SLCo.
"We also seek your co-operation and support on how the competition can be brought within the football ecosystem and work with us to achieve that objective.
"Your formal statement does, however, compel us to take protective steps to secure ourselves against such an adverse reaction, which would not only jeopardise the funding commitment under the grant but, significantly, would be unlawful.
"For this reason, SLCo has filed a motion before the relevant courts in order to ensure the seamless establishment and operation of the competition in accordance with applicable laws."
The decision to go public on the Super League follows a disagreement among some clubs over the level of commercial control they would have over the new-look Champions League.
Ceferin was speaking following the approval of reforms to the tournament, with the UEFA chief saying pointedly: "Teams will always qualify and compete in our competitions on merit, not a closed shop run by a greedy, select few."
The corporate structure of the Super League gives a clear indication of the leading figures behind the breakaway.
Real Madrid president Florentino Perez is the chairman of the new organisation, while Manchester United's co-chairman Joel Glazer is a vice-chairman.
So too is Juventus chairman Andrea Agnelli, who had been chair of the European Club Association and a member of UEFA's ExCo.
The PA news agency understands that on Monday Manchester United quit the ECA and executive vice-chairman Ed Woodward stepped down from his role at UEFA.
He had previously described the plans proposed by UEFA for the new-look Champions League as "ideal" but has now signed up to the Super League.
Ceferin was scathing about Woodward and Agnelli in particular, saying: "He's probably one of the biggest disappointments, or the biggest disappointment of all.
"I don't want to be too personal. But the fact is that I've never seen a person that would lie so many times, so persistently that he did was unbelievable.
"I spoke with him also on Saturday afternoon. He said, 'These are all only rumours. Don't worry, nothing is going on'. And then he said, 'I'll call you in one hour'. And he turned off the phone.
"I didn't have much contact with (Woodward) but he called me last Thursday in the evening saying that he's very satisfied with the reforms, that he fully supports the reforms, and that the only thing he would like to speak about is about financial fair play. And obviously he already signed something else."
The letter to FIFA and UEFA also said SLCo had secured a commitment to underwrite funding for the competition in the range of four billion euros (approximately £3.5billion), and JP Morgan confirmed to PA that it is financing the deal.
Any move to bar players from national team competitions as part of the dispute will be "vigorously opposed" by their global union FIFPRO, it said in a statement.