The Scottish champions exited the third qualifying round 5-4 on aggregate having thrown away a promising position not just after a 1-1 draw in Transylvania last week, but having led twice on the night at Celtic Park on Wednesday.
"We had the lead and we've let it slip through our own decision making," bemoaned Celtic manager Neil Lennon.
"We've only ourselves to blame. If you don't do the basics defensively well enough then at this level you get punished. We've let it go."
Celtic could have looked forward to a financial boost of around £30 million ($36 million) just for qualifying for the Champions League group stages had they clung on to the lead they held 10 minutes from time against Cluj and beaten Slavia Prague in the final qualifying round.
Instead, they must now win a playoff just to reach the Europa League group stages for the consolation prize of less than a third of that bounty.
However, it is the continuing blow to Celtic's prestige rather than the balance sheet that is of more concern to fans, who have grown frustrated at diminishing performances in Europe as the club has piled up cash reserves.
Celtic's most recent accounts showed £38.6 million in the bank even before receiving compensation paid from Leicester for manager Brendan Rodgers in February and the sale of Kieran Tierney to Arsenal for a Scottish record £25 million.
Those reserves have been accumulated on Rodgers' reaching the riches of the Champions League group stage in his first two of his three seasons in charge and the consistent sale of Celtic's best players.
Tierney followed the path forged by Victor Wanyama, Virgil van Dijk and Moussa Dembele in making his name in Glasgow before club record fees were secured in their departures.
Yet Celtic are now in a downward spiral. By not replacing that departed star quality adequately, they have missed out on Champions League cash for two successive seasons and will find it even more difficult to return to that promised land in the coming years unless more money is reinvested in the squad wisely.
A lack of competition in Scotland has allowed the Hoops to dominate for nearly a decade. This season they are aiming to match the Scottish record of nine titles in a row and have won three domestic trebles in a row.
However, Scotland's low coefficient means they now face four qualifiers just to make the Champions League and could be further impacted by proposed changes to make Europe's premier club competition more of a closed shop to smaller leagues from 2024.
The harsh reality of the financial gulf to Europe's top leagues means the limit of Celtic's ambitions in continental competition is just to reach the group stages of the Champions League.
But while Celtic can plead poverty compared to the Premier League and La Liga, there is no hiding their underachievement on the European stage in recent years against clubs even with a fraction of their own budget.
Cluj joined Malmo, Maribor and AEK Athens among those to have eliminated the first British club to win the European Cup from the Champions League in the last five years alone.