* FIFA warns breakaway Super League clubs must be 'in or out'
* UEFA say there is still time for rebel clubs to change minds
* Bayern and PSG reject notion of joining breakaway
* Football is being saved by the league - Real Madrid president
* UK PM Boris Johnson keen to talk to other nations involved
MANCHESTER, England, April 20 (Reuters) - FIFA president Gianni Infantino said on Tuesday that breakaway Super League clubs cannot be "half in, half out" of the established soccer system while his UEFA counterpart said it was not too late for those involved to step back from the brink.
European soccer's governing body UEFA has threatened to ban the 12 clubs, who include Manchester United and Real Madrid, from domestic and international competition, with Infantino adding his voice to the backlash.
"We strongly disapprove ... if some go their own way then they must live with the consequences of their choice, either you are in, or you are out. You cannot be half in and half out." Infantino told UEFA's congress in Montreux, Switzerland.
However, a Madrid court later warned UEFA and FIFA against imposing sanctions on club and players until it fully considers the Super League case.
England's big six -- Manchester United, Manchester City, Liverpool, Chelsea, Tottenham Hotspur and Arsenal -- came under attack from their domestic rivals for their involvement with the Super League, while the English Premier League said it "unanimously and vigorously" rejected the plans.
The Premier League said it was considering "all actions available" to stop the new competition which will guarantee membership for 15 clubs in contrast to the Champions League which requires qualification via domestic leagues.
The German Football Association (DFB) demanded the suspension of the 12 clubs until they reconsider.
"The clubs and their youth teams should be banned from all competitions until they think of their many supporters who have made them into top clubs in the world in the first place, and not only of their purses," DFB President Fritz Keller said on the official DFB Twitter account.
UEFA chief Aleksander Ceferin accused the breakaway dozen of contempt for smaller clubs.
But the Slovenian insisted there was still time for reconciliation.
"I would like to address the owners of some English clubs. Gentlemen, you made a huge mistake," he said. "Some will say it is greed others disdain, arrogance or complete ignorance of England's football culture but actually it doesn't matter.
"What matters is that there is still time to change your mind, everyone makes mistakes, English fans deserve to have you correct your mistake, they deserve respect."
Addressing UEFA's congress Ceferin made a point of thanking Paris St Germain president Nasser Al-Khelaifi whose club is not one of those involved in the breakaway.
"You are a real leader, a great man who respects football and its values," Ceferin said.
A statement issued by the Qatari Al-Khelaifi said any proposal without the support of UEFA would not resolve the issues currently facing the football community.
PSG are not the only big club to reject the Super League, as Bundesliga champions Bayern Munich also condemned the breakaway. "Our members and fans reject the Super League," said Bayern President Herbert Hainer in a statement.
Portuguese giants Benfica also issued a statement denying they were in discussions to join.
Manchester City manager Pep Guardiola, whose pre-match news conference was devoted to the seismic events partly initiated by his club, was candid in his opinion of the proposed league.
"It is not a sport where the relation between effort and success does not exist," he said, while saying those behind it had a duty to give more information.
"It is not a sport where success is already guaranteed or it doesn't matter where you lose."
Despite the universal wave of criticism, the instigators continued to argue that the breakaway was good for football.
In a letter to the club's commercial partners Milan chief executive Ivan Gazidis said: "We're confident that this new competition will capture the imagination of billions of soccer fans all over the world and will be a new, exciting chapter for the game."
Milan are one of three Italian clubs involved, the others being Inter Milan and Juventus.
The owners of the 12 teams have kept a low profile since Sunday's bombshell, with the first senior figure of any club involved being Real Madrid supremo Florentino Perez who earlier claimed "young people were no longer interested in football."
"Audiences are decreasing and rights are decreasing and something had to be done. We are all ruined. Television has to change so we can adapt," Perez, the new chairman of the Super League, told Spanish TV show El Chiringuito de Jugones.
The International Olympic Committee added its voice to the throng, warning that the existing structure of European sports is under threat by self-interest and pure commercialism.
"It is challenged by a purely profit-driven approach that ignores the... social values of sports and real needs in the post-coronavirus world," IOC President Thomas Bach said.
British Prime Minister Boris Johnson is also keen to speak to other countries who are involved, his spokesman said on Tuesday.
Asked whether the Prime Minister was planning to meet with his Spanish and Italian counterparts on the matter, the spokesman said: "We are keen to speak to everyone involved in this, from other countries too."
"We are fairly unequivocal that we don't want this to go ahead in the current form so we would welcome any club that wants to step back from this approach," he added, describing reports that some clubs were planning to step back as "speculation".
(Reporting by Peter Hall Editing by Christian Radnedge)