The final verdict in the case is not expected until next year.
ADVERTISEMENTPlans for a breakaway Super League have been dealt a fresh blow after an EU legal adviser backed FIFA and UEFA.
Advocate General Athanasios Rantos said the European Court of Justice should side with football's governing bodies and their regulations.
Rantos argued that the two international associations' rules blocking the breakaway competition were compatible with European Union law.
While the Super League's organisers were entitled to set up an independent competition, they could not also continue to play in UEFA and FIFA events without permission, he said on Thursday.
Rantos' opinion provides guidance to the European Court and, although not binding, is likely to be followed.
The Super League project collapsed in less than 48 hours in April 2021 after an outcry by fans, governments, and players forced Manchester United, Liverpool, Manchester City, Chelsea, Tottenham, Arsenal, AC Milan, Inter Milan, and Atletico Madrid to withdraw.
The remaining founders of the Super League -- Real Madrid, Barcelona, and Juventus -- have argued that UEFA breached European law by allegedly abusing its market dominance of football competitions.
But UEFA has stated that its rules protected the sport's essence and funded grassroots levels.
The body has "warmly" welcomed Rantos' opinion, saying it was “an encouraging step towards preserving the existing dynamic and democratic governance structure of the European football pyramid.”
The European Club Association, which represents Europe’s top football clubs, also stated that the advice "clearly rejected the efforts of a few to undermine the foundations and historical heritage of European football for the many.”
The EU's top court is expected to issue a final ruling next year.