Scottish giants Celtic will discover if their Europa League reinstatement stands next Tuesday after UEFA confirmed Sion have appealed against their expulsion from the competition.
Sion were kicked out of the Europa League after Celtic complained about the club fielding players signed while they were subject to a transfer ban.
The Swiss side, who beat Celtic 3 - 1 on aggregate to qualify for the tournament, continue to fight their expulsion and their latest appeal will be heard on September 13, the day before Celtic had planned to fly to out for their opening match against Atletico Madrid.
Sion had revealed on Monday they planned to appeal and UEFA were expected to convene a panel on Friday, but the delay throws up even more uncertainty for the affected clubs and Celtic fans hoping to travel to Spain.
The Swiss club would have one more conventional avenue of appeal if their second UEFA hearing fails.
The Lausanne-based Court of Arbitration for Sport would be able to overturn UEFA's decision if they found in favour of Sion.
But the club's controversial president, Christian Constantin, has vowed to take on the governing body in the civil courts, although their first attempt failed on Thursday.