Neil Lennon blasted his team after Celtic crashed out of the Champions League with defeat to CFR Cluj.
Celtic, after drawing 1-1 in Romania, led twice on the night but fell to a 4-3 defeat at Celtic Park.
It means the Scottish champions since 2012 will not feature in the group stages of Europe’s elite competition.
"We had the lead and we've let it slip through our own decision making," said Lennon.
"The goals we conceded are crazy. You've got to do the basics well - you've got to stop crosses, close people down, get your head on things - and it was almost as if we scored and wanted to switch off.
"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."
The Hoops made a storming start to the second half to go 2-1 ahead through goals from James Forrest and Odsonne Edouard but Scott Brown’s handball allowed Billel Omrani to net from the spot.
Ryan Christie soon put Celtic back in front but Omrani quickly levelled in the 80th minute to put the Romanians ahead on away goals.
George Tucudean then netted with the last kick of the game to seal a 5-4 aggregate win in the third qualifying round.
Additional by PA:Media
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