Top players will be barred from playing for their national teams in events like the World Cup if their clubs join a breakaway league, the major governing bodies warned on Thursday.

The announcement by FIFA and soccer’s six regional confederations follows weeks of talks and months of disquiet after the revelation of plans hatched by some of the world’s richest and most popular clubs — led by Real Madrid and Manchester United — to create a so-called Super League. That competition, which would be controlled by the teams, could at a stroke render irrelevant the Champions League, European soccer’s immensely popular club competition.

Talks about a new league come as discussions with European soccer’s governing body UEFA over a new format for the Champions League beginning with the 2024 season are close to completion. Some senior leaders at UEFA are hoping to announce the changes, the biggest to the event in a generation, as soon as the organization’s annual meeting next month.

FIFA said in a statement that a Super League “would not be recognized by either FIFA or the respective confederation. Any club or player involved in such a competition would as a consequence not be allowed to participate in any competition organized by FIFA or their respective confederation.”

According to documents reviewed by The New York Times, plans for the breakaway European Super League, a project that has been mooted for decades, gathered pace since the summer. Top clubs sought to take advantage of uncertainty in the soccer industry caused by the coronavirus pandemic to forge a new path that would insure a degree of financial stability for them but almost certainly lead to a loss in the value and revenue for teams excluded from the project.

Under the proposals, the Super League, which would be played in the middle of the week, would have 16 top soccer franchises as permanent members and add four qualifiers from domestic competitions. The clubs would be split into two groups of 10 with the top four teams in each group qualifying for the knockout stages, culminating in a final that would take place on a weekend. The event would, according to the documents, generate hundreds of millions of dollars in additional revenue for the participating teams, already the richest clubs in the sport. (An alternative version of the plan has 15 permanent members and 5 qualification spots.)

The group has already entered into discussions with JPMorgan Chase&Co. to raise financing for the project, according to people with knowledge of the matter. A spokesman for the bank declined to comment.

The clearest public indication of how advanced the talks among the clubs are came when Josep Maria Bartomeu, the former president of Barcelona, announced in October that his team had agreed with the leaders of what he described as Europe’s other “big clubs” to participate in a European Super League. Bayern Munich, Germany’s biggest team, spoke out this week against a breakaway, but should other top teams find an agreement it would be unrealistic for that club not to be involved as well.

The project has long been the brainchild of Florentino Perez, the president of Barcelona’s rival Real Madrid. Leaked documents from 2018 revealed he had drawn up plans with a Spanish consultancy for a new competition and then held a meeting with FIFA’s president Gianni Infantino in 2019 to discuss the plans further, telling him that teams from the Super League competition would be willing to participate in FIFA’s expanded World Cup for clubs, a quadrennial event that Infantino believes could grow to become one of the most important properties in all of sports.

Since the summer, Perez found a new ally in Joel Glazer, the chairman of Manchester United, who has also joined forces with the American owners of Liverpool in an effort to force through changes to the Premier League that would benefit his team. Glazer has been promoting the idea of the Super League, according to people with knowledge of the discussions. A spokesman for United said the team would not comment.

The joint announcement by FIFA and the six confederations follows talks on Monday between Infantino and his counterpart at UEFA, Aleksander Ceferin. The two men have had a bumpy relationship since 2018 when Infantino announced his ambitions for FIFA’s own club competitions and growing suggestions of his involvement in the breakaway talks. Infantino has always publicly denied any interest in supporting a European breakaway.

Ceferin has frequently launched broadsides against the Super League discussions. “It would be hard to think of a more selfish and egotistical scheme,” he said after one iteration of a breakaway was discussed. “It would clearly ruin football around the world; for the players, for the fans and for everyone connected with the game — all for the benefit of a tiny number of people.”

UEFA’s proposals for the new version of the Champions League go a long way to meeting the demands of the biggest clubs for an expanded tournament. If agreed, the tournament will feature 36 teams instead of the 32 it currently does, with two of those places reserved for teams that have been historically successful in European competition but failed to meet the qualification criteria. That would mean the possibility of a return to top tier action for the likes of A.C. Milan, a soccer heavyweight that has fallen on hard times. UEFA’s reforms would also scrap the current opening stage in which teams are separated into eight groups of four, and instead place them into one table, with qualifiers for the knockouts determined by results after each team has played as many as 10 games.

Access to the competition, unlike the Super League, would largely be from the domestic leagues, ensuring they remain relevant.

The European Leagues, an umbrella group for many of the continent’s leagues, issued a statement endorsing the declaration against the Super League by the governing bodies.

“The European Leagues’ board of directors has discussed the initiative of some European football clubs to create a closed European Super League for a limited number of clubs similar to those franchise models operating in North America,” the group said.

“UEFA and the other football Confederations from all over the world have, together with FIFA, published a strong statement against this initiative and our member leagues are unanimously supporting that statement.”