Celtic captain Scott Brown has urged UEFA to reinstate the Scottish giants in the Europa League.
The Glasgow club were beaten 3-1 on aggregate by Sion in the play-offs but were given hope of a reprieve by UEFA president Michel Platini, who said the Swiss club had ''not respected the rules of the transfer ban'' by signing five players who are, in the eyes of FIFA, ineligible to play due to a transfer embargo.
Celtic played both games under protest and UEFA's control and disciplinary body could make a ruling on the case on Tuesday.
Indeed, Brown has no doubt that Celtic should be taking Sion's place in a group which includes Atletico Madrid, Udinese and Rennes.
''Yes, I think we should be,'' said the Scotland midfielder. ''They played three players that shouldn't have been allowed to play and at the end of the day you can't do that, and hopefully UEFA see that as well.''
Scottish Football Association president Campbell Ogilvie has pledged his organisation's backing to Celtic in their quest, and confirmed Celtic had sought and received help from the SFA.
''Celtic made contact with the SFA, as any member club would do, and the SFA have been backing Celtic,'' Ogilvie said. ''The case is being heard this week and as a governing body we would always back one of our clubs in one of these cases. If there is a breach of rules then UEFA will certainly take whatever sanctions are necessary, but the SFA would certainly back a member club in this case.''
Ogilvie added: ''The decision is for UEFA but if someone has breached regulations and has been proved to have breached regulations then obviously a sanction should be taken, but that's obviously outwith our remit.''
It is likely to be next week at least before the issue is fully resolved.
The UEFA spokesman said: ''The first stage is the UEFA control and disciplinary body. After that there is the ability to appeal the decision and a club is given three days to do that from the time they get the full written submission of the decision.
''The last stage is CAS (Court of Arbitration for Sport) and a date would have to be set for that. But it is a complex case.''