Premiership Rugby have stated that other teams are welcome to enter the new breakaway tournament proposed by the English and French rugby unions.
The top-flight clubs have called for a new European competition to be created as a replacement for the Heineken Cup.
"If we can't reach an outcome involving all the European clubs, we at least have to set up a competition involving the English and French clubs," BBC Sport quotes chief executive Mark McCafferty as saying.
"If others want to come into that competition, then we can look at that, but we have to get on and prepare."
Talks to continue the Heineken Cup have come to a halt.