Benetton Treviso have given notice that their involvementin the tournament will end when their participation agreement expires in June.
If they and the Welsh both follow through on their threats, it would make life almost impossible for the Scottish Rugby Union, which has invested heavily in its two pro clubs but could be left without any viable cross-border tournaments for them to compete in.
In a statement posted on Treviso's website, the blame is laid squarely on the uncertainty surrounding European competition at all levels. There is no agreement on the future of the Heineken Cup and uncertainty over the future of the existing Celtic/Italian league competition as the Rabobank is pulling out of its sponsorship deal at the end of the season.
There is also an internal row between the Welsh Rugby Union and the body representing the country's four district teams which means no-one can be sure what teams will be taking part.
In a reference to the stalled Heineken Cup talks, Trevison stated they has made their move "in light of the international situation that further prolongs a decision".
They added that "the absence of certainty about the future forms of organisation, participation and regulations relating to the RaboDirect PRO12 league" have added to the pressure.
There is also an Italian dimension to Treviso's move. While the Italian Federation [FIR] fully funds the other PRO12 side, Zebre, it has left Treviso largely to pay for itself. When Italy decided in 2009 to join forces with the Celtic League, the FIR did not include Treviso and changed its mind only after a campaign by the club and the collapse of a planned franchise in Rome.
Though Treviso has always been the stronger of the two Italian sides in the competition, the club has never come close to winning anything.
Treviso's statement may strengthen the hand of Alfredo Gavazz, the new president of the Italian Federation. He is in negotiations with the Celtic countries regarding the terms of Italy's involvement and is particularly anxious to end the subsidy of almost £2m a season which allows Italian teams to be compete in the league.
Gavazz has threatened to pull both Italian teams out of the competition and has already published plans for an eight-team professional and semi-professional domestic league. It is a move which Treviso has backed, albeit cautiously. In their statement, the club claimed it is "willing to consider, and possibly participate in any competition and/or challenge that the FIR intends to promote".