Celtic's Champions League hopes were ended after a 2-1 qualifying defeat by AEK Athens in Greece saw them lose 3-2 on aggregate.
Boss Brendan Rodgers, who had taken the Scottish champions to the group stages of the competition in his first two years in charge, knew the third qualifying round tie was his biggest qualifying challenge to date following the 1-1 draw in the first leg in Glasgow last week.
Within six minutes his side were trailing to a Rodrigo Galo strike and it looked a forlorn task when Croatian striker Marko Livaja headed in a second five minutes after the break.
Hoops substitute Scott Sinclair - on for Australia's Tom Rogic - pulled a goal back in the 78th minute but despite a grand finale the visitors could not fashion a second which would have put them through on away goals.
Dropping down to the Europa League, where they will play Latvian side Spartaks Jurmala or Lithuanian side Suduva, is a huge blow for Celtic who will miss out on the prestige - not to mention the vast sums of money - to be earned in the Champions League.
Brazilian midfielder Galo put AEK ahead when he swept the ball past keeper Celtic Craig Gordon from 12 yards.
But Celtic soon took control, with Socceroos star Rogic and Leigh Griffiths both having luckless efforts on goal before the latter sent a fine Callum McGregor cross inches past the post from eight yards.
Any positivity Celtic's response elicited evaporated early in the second half when Galo's free-kick to the back post was headed back across goal by Vassilis Lampropoulos for Livaja to head past Gordon.
Again Celtic responded positively and only a brilliant save by AEK keeper Vassilis Barkas prevented Jozo Simunovic's header from a Kieran Tierney cross speeding in at the near post.
Rodgers brought on Moussa Dembele as Celtic kept piling forward and minutes after Sinclair came on, he gave the Hoops hope when he headed in a Tierney cross.
But the Greeks held out in the nervy final minutes, despite Simunovic coming agonisingly close with a flick in the last of five added minutes.