Swiss club Sion, still fighting UEFA's decision to kick them of the Europa League for fielding ineligible players, could face compensation claims if they win reinstatement to the competition.
Atletico Madrid, Rennes, Celtic and Udinese, who might have to play extra games against the Swiss side, have asked the Court of Arbitration of Sport (CAS) to make Sion pay damages to them should they be readmitted.
Atletico spokesman Juan Jose Anaut told Reuters on Friday that the four clubs, who make up Europa League Group I, had made a joint petition to CAS, based in Lausanne, over the extra costs and inconvenience Sion's inclusion would cause.
CAS was not immediately available to comment.
It is the latest development in the battle involving Sion who have taken their case to a civil court after UEFA expelled them for fielding ineligible players in the play-off tie against Celtic, which the Swiss side won.
Celtic took Sion's place in Group I but the civil court in Vaud canton issued an injunction ordering UEFA to reinstate the club.
"Like Rennes, Udinese and Celtic, Atletico feel directly affected by this ruling, which does not fit in with sporting regulations," Atletico lawyer Juan de Dios Crespo told the Spanish sports newspaper As.
UEFA has drawn up several possible ways of reincorporating Sion, one of which would involve cancelling all 12 matches played so far - four by each team.
"This would mean that we travelled all the way to Rennes in France and Udine in Italy for nothing," said Anaut. "We would also have to find more space in the calendar which is already full."
CAS have agreed to hold a hearing into the case between UEFA and Sion on November 24, however the Swiss club have not yet indicated whether they will take part.
Sion signed six new players in the summer despite being subject to a transfer ban imposed by FIFA for poaching an Egyptian player from his old club in 2008.
Some of the players then took part in the tie against Celtic.comments