Celtic could face more European uncertainty despite Legia Warsaw's failure to persuade UEFA to overturn their effective expulsion from the Champions League.
Celtic stepped up preparations to face Maribor in Slovenia in the Champions League play-offs on Wednesday after UEFA's appeals body upheld an earlier decision by its disciplinary body to award Celtic a 3-0 second-leg win over Legia after the Poles fielded an ineligible player.
But the Polish champions, who are now due to face Kazakhstan's Aktobe in the Europa League, vowed to take their case "promptly" to the Court of Arbitration for Sport.
And the Swiss-based court stated that it could hear the case early next week.
CAS general secretary Matthieu Reeb told STV: "We can organise a fast-track procedure which takes into account the time constraints and whatever kind of decision, be it an order or final award, and we can try to do it within the appropriate time.
"It's possible if the parties are prepared to do that. All our councils, parties, all people involved in this matter should be available on short notice.
"If there is an appeal, it should be filed as soon as possible so that the start of the procedure is not delayed. We can also use Saturday and Sunday to work on this case. It is feasible but there is no time to lose.
"It depends on what is requested by Legia. If the request is to declare the UEFA decision illegal or contrary to the rules, it is a legal discussion and we should be able to provide an answer after reviewing not only the UEFA decision and the rules, but also the arguments of the parties. This can be done on a short time frame."
Reeb added: "If Legia would request CAS to render a decision by way of provisional measures, this could at least give an answer to the case before the start of the competition.
"But if the parties are also ready we could organise a hearing say for example for Monday so that the case is resolved for all."
The Polish club were found to have fielded an ineligible player, Bartosz Bereszynski, in the second leg of their third qualifying round clash against the Scottish champions, which they won 2-0 to follow a 4-1 first-leg success.
Legia thought the defender had served a three-match ban but it emerged they had failed to register him for the previous round.
Club owner Dariusz Mioduski said: "Till the last moment we hoped that the spirit of sport wins, we find the decision extremely unfair.
"However we expected that decision and were prepared for it. We are to appeal to the CAS promptly.
"We will use the full appeal procedure, in order to get back our result that was fairly gained on the pitch.
"We will certainly fully subordinate to the final verdict. But I still hope that football will win, as well as the values it is based on: fair-play and respect to the on-the-pitch result."