Celtic will discover if their Europa League reinstatement stands on Tuesday - two days before their scheduled opener against Atletico Madrid - after Sion submitted an appeal against their expulsion late on Thursday night.
UEFA confirmed an appeal hearing would be heard on September 13, the day before Celtic had planned to fly to Spain.
Sion had revealed on Monday they planned to appeal and UEFA were expected to convene a panel today, but the delay throws up even more uncertainty for the affected clubs and Celtic fans hoping to travel to Spain.
Sion, who were thrown out for fielding ineligible players, will take their case to UEFA's appeals body after the control and disciplinary body ruled against them last week.
The Swiss club beat Celtic 3-1 on aggregate in the play-offs.