The French Rugby Federation (FFR) has indicated it will oppose Anglo-French plans to establish a replacement for the Heineken Cup.
Although Premiership Rugby chief executive Mark McCafferty expects Celtic and Italian sides to join the planned 'Rugby Champions Cup', the FFR is backing European Rugby Cup.
Premiership Rugby and the Ligue Nationale de Rugby require approval from the Rugby Football Union, FFR and International Rugby Union to go ahead with their breakaway competition, but the FFR is unwilling to grant its support.
"No match or international competition involving French clubs can be organised outside the framework of the FFR and without its prior agreement," a statement by FFR read.
"The FFR has always been and will remain a major player in the European cups organised by European Rugby Cup and backs proposals to permit the continuity and development of these.
"If the FFR is in favour of an improvement in the European cups, their organisation can only be envisaged under the edict of the European federations which make up ERC.
"The statement released by the clubs appears therefore irrelevant and inappropriate."
ERC appeared to be in full retreat as its appointment of an independent mediator was met with a statement of Anglo-French intent.
McCafferty revealed that PRO12 sides expressed interest in joining the breakaway.
Premiership Rugby and Ligue Nationale de Rugby plan to finalise the structural detail of the Rugby Champions Cup when it is assured of who will be involved.
"Before we can release more information we need to know over the next few weeks which other teams will be joining the competition," McCafferty said.
"Once we know the final, or close to final, numbers then we'll settle on the competition formats.
"Various people have approached us about the possibility of joining and we've indicated to them that we'll keep their names confidential.
"We've heard that other people want to be involved in European competitions, that's why we've left the door open and expect it to be more than an Anglo-French competition.
"Once people saw on September 10 that we would seek an alternative to the Heineken Cup, interest has been expressed in at least knowing exactly what will be involved."