The European Super League Company (ESLC) and its backers A22 Sports Management had argued that UEFA and FIFA's attempts to block its formation and sanctions against the clubs involved breached the European Union's (EU) competition law.

However, Rantos found that in his opinion "the FIFA-UEFA rules under which any new competition is subject to prior approval are compatible with EU competition law."

He also declared that the competition rules did not prevent either body, their Member Federations or national leagues from threatening sanctions against clubs to pursue a project to establish a new competition.

Rantos added that EU competition rules "do not preclude the restrictions, in the FIFA Statute, concerning the exclusive marketing of the rights relating to the competitions organised by FIFA and UEFA", and "EU law does not preclude the FIFA and UEFA Statutes which provide that the setting up of a new pan-European interclub football competition is to be subject to a prior approval scheme."

He said that the ESLC "is free to set up its own independent football competition outside the UEFA and FIFA ecosystem", but cannot create a parallel competition and continue to participate in FIFA and UEFA competitions without their prior authorisation.

The CJEU advocate general's opinion is non-binding, with a final verdict expected to be delivered by a 15-member Grand Chamber in spring 2023.

UEFA said it "warmly welcomes" Rantos' opinion, and said it "is an encouraging step towards preserving the existing dynamic and democratic governance structure of the European football pyramid."

"The opinion reinforces the central role of federations in protecting the sport, upholding fundamental principles of sporting merit and open access across our members, as well as uniting football with shared responsibility and solidarity," a UEFA statement read.

"Football in Europe remains united and steadfastly opposed to the European Super League, or any such breakaway proposals, which would threaten the entire European sports ecosystem.

"While we await the Court’s final judgment due next year, UEFA, as a public interest, not-for-profit governing body, will continue to be fully focused on its mission to develop football for all, in close cooperation with national associations, leagues, clubs, players, fans, EU institutions, Governments and other relevant stakeholders who have the true values of football at heart."

FIFA has also said it "welcomes" Rantos' opinion "in which he confirms the standing and legitimacy of FIFA and UEFA to approve any new football competitions."

The European Club Association (ECA) said that Rantos' opinion "reinforces ECA’s long-standing opposition to the European Super League and any breakaway project."

In October, UEFA renewed an accord with the European Commission endorsing the European sports models, which is said to promote solidarity across different levels of sport, ensuring that revenue generated by professional competition is reinvested into developing football at grassroots levels.

In July, UEFA lawyer Donald Slater claimed at the CJEU in Luxembourg that the European Super League is a "textbook example of a cartel."

A22 Sports Management appointed German businessman Bernd Reichart as its new chief executive in October as it sought to revitalise the project.

Reichart claimed that Rantos' opinion is "one step in an ongoing case, and we are pleased with the recognition of the right of third parties to organise pan-European club competitions."

The proposal for a breakaway Super League was revealed in April 2021, but sparked an outcry from fans, domestic leagues, UEFA and FIFA.

Nine of the clubs involved were forced to withdraw in Manchester United, Liverpool, Manchester City, Chelsea, Tottenham Hotspur, Arsenal, AC Milan, Inter Milan and Atlético Madrid.

However, Spanish clubs Barcelona and Real Madrid and Italian giants Juventus remain publicly committed.

Since the effective collapse of the European Super League project, UEFA's Executive Committee has voted through major changes to its flagship men's Champions League, with the club tournament expanding from 32 to 36 teams from the 2024-2025 season.

Controversial plans to grant two of these additional places to clubs based on their historic performance in European competition were dropped after much criticism, and they are instead set to go to the highest-placed non-qualifying teams in the two countries with the best collective performance by their clubs in the previous season.

UEFA also plans to move away from the eight groups of four followed by a knockout stage format to a so-called "Swiss system", which involves a single league phase in which clubs will face eight of the other 35 teams.

The eight top-ranked clubs advance to the knockout rounds, with those placed ninth to 24^th competing in two-legged playoffs to secure their place in the last 16.