Celtic will continue in the Europa League group stages even if Sion are successful with an appeal to the Court of Arbitration for Sport. Sion were expelled from the tournament for fielding ineligible players in their play-off victory over the Hoops and lost an appeal against their expulsion later that month.
A statement from UEFA read: "The first option assumes the cancellation of all previous games in Group I of the UEFA Europa League, and for a set of new games to be played within a group of five, following the rules of the former UEFA Cup group stage with teams playing against each other either at home or away.
"These matches could then be played between November 24 and December 22.
"The second option allows for the integration of FC Sion into Group I as an additional fifth team, but that the results and points of the games already played in the group remain.
"Eight additional matches would have to be played, starting at the end of November and finishing in February 2012.
"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 play-off round still to be defined."
The statement went on: "Of course all these scenarios have one thing in common, and that is a strong impact on the other clubs in the competition.
"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.
"As none of the suggested scenarios proposes a first matchday before November 24, UEFA believes there is a strong possibility of obtaining a decision based on the merits of the case in CAS, provided that FC Sion accepts the CAS accelerated procedure."