UEFA makes provisions for Sion reinstatement
All of the options would require substantial changes to Group I where Celtic took Sion's place after the Swiss club were kicked out of the competition by UEFA for fielding ineligible players in a preliminary round tie against the Scottish club.
UEFA said the first option would be to cancel all the previous matches played so far in the group which also features Atletico Madrid, Udinese and Stade Rennes.
Under this option, the group would start from scratch with five teams playing each other once between November 24 and December 22, UEFA said.
A second option would add Sion to the existing group but results and points of matches already played would remain valid and it would continue to be played on a home-and-away basis.
"Eight additional matches would have to be played, starting at the end of November and finishing in February 2012," said UEFA.
"The other options, mainly valid in the case of a late reintegration, assume that FC Sion could be integrated directly into the round of 32, following a qualifying playoff round still to be defined."
UEFA added: "All the scenarios studied by UEFA offer the best possibility of reintegrating FC Sion while preserving the interests of all other clubs, limiting damages to the competition, and offering enough time to ensure a safe organisation of these additional games.
Sion won an injunction at a court in Vaud canton ordering their reinstatement to the competition.
UEFA bans clubs from taking sporting matters to civil courts but is based in the same canton as the court and could have risked legal action if it had ignored the injunction.
UEFA said none of the solutions could be implemented without the agreement of the clubs who Sion would have to play, possibly during a period usually reserved for the winter break.
"f course all these scenarios have one thing in common, and that is a strong impact on the other clubs in the competition," said UEFA in a statement.
"UEFA therefore underlines the fact that the other clubs may accept these possibilities only after a decision made by the Court Arbitration for Sport (CAS), as CAS is the only authority they have all accepted as competent to rule on sporting matters in the UEFA Europa League."
However, UEFA added that the case could only go to CAS with the agreement of Sion.
It added that none of the options would involving kicking Scottish club Celtic out of the competition.
Sion signed six new players in the summer despite being subject to a transfer ban imposed by FIFA after being found guilty of inducing an Egyptian player to break his contract with his previous club to join them in 2008.
A civil court in Switzerland ruled they could play in domestic matches and the Swiss League accepted that decision.
Sion then fielded some of the players in a Europa League qualifier against Celtic which they won 3-1 on aggregate. Celtic protested and were declared winners of the tie.