Federation Internationale de Football Association president Gianni Infantino has warned that any players taking part in a breakaway European super league would be excluded from the World Cup and other worldwide tournaments.
German magazine Der Spiegel reported last week that Bayern Munich and their chairman Karl-Heinz Rummenigge attempted to lead some of the continent's biggest clubs into a new competition.
European Leagues - an organisation that acts on matters of common interest regarding clubs from the 32 professional leagues it represents - has already spoken out against the idea of a "closed and franchised style" competition.
Infantino, meanwhile, defended his role in another of the stories revealed by Der Spiegel, which alleged Manchester City struck a secret deal with European football's governing body UEFA in 2014 to avoid a potential Champions League ban for breaching Financial Fair Play regulations.
"You are either in or you are out", the head of the world soccer body told a group of global reporters.
"Either you are in or you are out", Infantino said, listing the World Cup, European Championship and national leagues as competitions that players from breakaway teams could be excluded from. "That would be the general approach we would follow, but of course lawyers can debate this for a long time".
Infantino said the Club World Cup was his answer to any breakaway attempt, presenting it as a competition that would generate more revenues for the clubs but also benefit the soccer community.
"People are still quite reasonable", Infantino added, however.
"We worked with the information we had at the time".
Also Wednesday, Infantino addressed the "Football Leaks" documents that showed him being pressured by wealthy clubs during his time as UEFA's top administrator to ensure they avoided a Champions League ban for breaking "Financial Fair Play" rules created to curb overspending.
A 48-team World Cup would entail 80 games, meaning up to six matches would have to be played on some days during the group stages to fit the 28-day window.
Infantino recently said the idea was "feasible" - but appeared more cautious in his latest comments. We do. It is decided in March, but I am not a prophet and I don't know if it will be approved.
The Club World Cup, now an annual tournament with seven teams, could become a four-yearly event featuring 24 clubs instead. "It is a hard challenge".
"It will be a very, very hard challenge to do it only in Qatar". There are documents. But it is our responsibility to find ways for football to be united.
"We are in discussion with Qatar", said Infantino, who said the tournament would need to spread to neighbouring countries. "Certainly small but what is wrong in discussing it?" he added.