A breakaway European Super League would have "serious and lasting implications" for professional football across the continent, the European Leagues group (EL), which represents domestic leagues, said on Tuesday.
German magazine Der Spiegel and European Investigative Collaborations, a network of international media, reported on Friday that plans for a Super League involving clubs such as Real Madrid and Manchester United were back on the table.
Citing leaked documents, Der Spiegel said a fresh plan had recently been drafted for Real Madrid by Spanish company Key Capital Partners. The plan foresees 11 top European clubs creating a Super League in 2021.
Key Capital Partners and Madrid have not commented on the report, while the European Club Association, which represents more than 200 European clubs, said it was not aware of discussions by clubs to develop a breakaway league.
The EL, which represents 25 domestic leagues including England's Premier League, Germany's Bundesliga and Spain's La Liga, voiced its "strong opposition" to any such plan on Tuesday.
"The European Leagues note the ongoing rumours and speculations around the possible creation of a European Super League by the big European professional clubs," it said.
"[EL] has consistently voiced its strong opposition to the creation of any 'closed and franchised style' Super League.
"The Leagues supports the European sports model based on a pyramid structure where the mechanisms of promotion and relegation and the sporting merits of clubs are at the core of any competition."
The statement said domestic football was at "the heart of the game throughout Europe" for players, clubs and fans.
"Proposals for a closed Super League will have serious and lasting implications for the long term sustainability of professional football in Europe," it said.
It said it "fully supported" European football's governing body UEFA in the organisation of the Champions League and Europa League and "shares with UEFA the common principle of protecting and enhancing competitive balance in European football."
The EL recently presented its own suggestions for the format of European club competitions in the next three-year cycle, starting in 2021, which it said would ensure a more equal distribution of revenue.
According to Der Spiegel, the 16-team Super League would replace the Champions League from 2021 and include 11 "founders" who could not be relegated for the first 20 years.