UEFA has reinstated Celtic to the Champions League playoffs in a last minute switch after qualifying-round opponent Legia Warsaw were punished for fielding an ineligible player as a late substitute.
Legia, who had eased past Celtic 6-1 on aggregate, are weighing an urgent appeal before play-off matches kick off on August 19.
Club official Dominik Ebebenge blamed human error for failing to register the player in question for previous qualifying games - meaning those did not count towards his three-game suspension.
"The proportion between the error and the consequences is unimaginable," Ebebenge told reporters after receiving UEFA's verdict one hour before the play-offs draw.
The UEFA decision could potentially cost the club millions of dollars in Champions League prize money.
UEFA pays clubs $2.8m for the play-off round and a basic $11.5m award for reaching the group stage.
Celtic have now been drawn against Slovenian champion Maribor in the two-legged play-offs.
Arsenal were drawn against Besiktas of Turkey and two-time European champion Porto will play Lille of France.
A high-class Italy versus Spain clash pair Napoli against Athletic Bilbao.
Zenit St Petersburg were drawn against Belgium's Standard Liege, and Copenhagen will face Bayer Leverkusen.
First-leg matches will be played on August 19-20, and return matches on August 26-27.
The 10 play-off winners advance to the 32-team group stage drawn on August 28 in Monaco.