As Shamrock Rovers became the first Irish side to make the group stages and were rewarded with money-spinning ties against Tottenham, Uefa insiders said Celtic would be allowed back into the competition if the Swiss side Sion were banned for breaching transfer regulations.
Celtic lost 3-1 at Sion on Thursday, but the Swiss side included five players acquired by the club during a transfer ban imposed by Fifa after breaching rules over the signing of the Egypt goalkeeper Essam El-Hadary three years ago.
Sion have since been found by Fifa, the court of arbitration for sport (CAS), and the Swiss supreme court to have breached the transfer ban but are challenging the decision in a local court.
The Uefa president, Michel Platini, said: "What is happening there are rules that have not been respected. FC Sion has not respected the rules of the transfer ban – they signed players and then played those players."
Gianni Infantino, the Uefa general secretary, said the case would be dealt with by the organisation's control and disciplinary body, with a hearing expected on Tuesday. "The civil court ruling does not affect Uefa. We will look at our rules and the Fifa rules. There is a ruling by Fifa, CAS have ruled, it went to the Swiss supreme court and everything was confirmed but it has been challenged again," he said.
"It is an interpretation question which is complicated – whether a two transfer-window ban means two transfer windows or parts of several transfer windows."
If Sion are banned and Celtic reinstated, the Scottish team will be placed in a challenging group with Udinese, Rennes and the 2010 Europa League winners, Atlético Madrid.
The Celtic manager, Neil Lennon, said he would have no problem accepting a place through the back door if his side are reinstated. "We have sent in letters last week and handed one to the delegate," he said. "There is a hearing on Tuesday and we will know the outcome after that. But if clubs are breaking the rules then every club should break the rules."
Platini said he was "very disappointed" with the performance of Scottish clubs, after none progressed beyond August in European competition for the first time.
"They have such great clubs and it is a shame none of them have qualified but these things are decided on the pitch," he said. "The Scottish league have to look at this situation very seriously now."
Shamrock Rovers will look into the possibility of moving their home tie against Spurs, in a group that also contains a long-distance trip to the eastern Russian city of Kazan, to the Aviva Stadium.
The chairman, John Roche, missed the draw after celebrating his team's win against Partizan Belgrade until 5am and then having to contend with delays, instead following it on his phone as he raced to Monaco from the airport.
"It's been an unbelievable two days. Five years ago we were relegated, then the fans took over the club," he said.
"We won the league for the first time in 16 years last season and hopefully now this will show people that we play a good style of football. It's not really about the money but it's the whole razzmatazz and the profile of the football club."
Stoke City face journeys to Ukraine, Turkey and Israel in their first European campaign for 37 years and their manager, Tony Pulis, admitted that would prove a challenge.
"I'm just amazed those three countries are in Europe. It will be a logistical nightmare but it's all very new to us," he said. "We knew when we qualified it would be a tough programme and the squad would be tested. It's a little bit unfortunate that we have such long journeys but we just have to get on with it.
"We're still looking to strengthen the squad next week and whenever possible we will stick with the policy of playing strong teams in the Europa League."
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