The European Club Association (ECA) has condemned the proposed Super League while announcing a new executive committee including representatives from Paris Saint-Germain and Bayern Munich.
A 12-team group including some of European football's biggest names confirmed plans for a breakaway competition on Sunday, with those founding members guaranteed to be involved every year regardless of their domestic performances.
The competition has received widespread criticism from governing bodies, former players and fan groups alike.
UEFA president Aleksander Ceferin branded the European Super League as a "disgraceful, self-serving proposal" fuelled by greed, as well as confirming players from the clubs involved will be banned from playing international football.
After a meeting of its executive board on Monday, the ECA made clear it remains the only "legitimate and fully recognised voice" for Europe's leading teams.
"The board was unanimous in its condemnation of the actions of the departing members, which it holds to be self-serving and to the detriment of the game's wellbeing and in clear opposition to ECA's values," a statement read.
"We believe that European club football can be reformed from within the system to achieve the collective best interests of all stakeholders in the game.
"The board reiterated ECA's clear position as the only legitimate and fully recognised voice of the leading clubs in Europe and, as such, has taken a number of decisions to ensure that it is able to continue to perform its role efficiently and effectively."
The ECA also announced PSG chairman Nasser Al-Khelaifi will be involved on a new-look executive committee, as well as Bayern representative Michael Gerlinger. Neither of the clubs were involved in the European Super League.
They will be joined by Edwin van der Sar (Ajax), Dariusz Mioduski (Legia Warszawa), Aki Riihilahti (HJK Helsinki) and Michele Centenaro (the ECA's independent board member).
Meanwhile, UEFA announced plans for Champions League expansion on Monday, the tournament set to see an increase to 36 teams from the 2024-25 season onwards.
"We are pleased that UEFA club competitions reform has reached this important milestone," the ECA said on the structural changes to the competition.
"The agreement of new competition formats will create a greater number of high quality, relevant, exciting European matches for fans and increase participation for clubs at all levels - principles and targets that ECA laid out back in the Spring of 2019 when we embarked on this reform journey.
"Moving forward, the entire ECA executive board's focus will be on pursuing efforts to conclude arrangements with UEFA around its renewed relationship post-2024 as we look to shape European club football for the years ahead."
Bayern CEO and honorary ECA chairman Karl-Heinz Rummenigge, who is to replace Andrea Agnelli as one of two representatives on the UEFA executive committee, made clear that the Bundesliga club support the revamped Champions League structure.
"Bayern has not been involved in the plans for creating a Super League. We are convinced that the current structure in football guarantees a reliable foundation," Rummenigge said.
"Bayern welcomes the reforms of the Champions League because we believe they are the right step to take for the development of European football. The modified group stage will contribute to an increase in excitement and the emotional experience in the competition.
"I do not believe the Super League will solve the financial problems of European clubs that have arisen as result of the coronavirus pandemic.
"Rather, all clubs in Europe should work in solidarity to ensure that the cost structure, especially players' salaries and agents' fees, are brought in line with revenues, to make all of European football more rational."