Manager Ronny Deila admitted he was disappointed in the lack of "commitment" and "energy" from his Celtic players following their crushing 4-1 defeat to Legia Warsaw in the first leg of their Champions League third qualifier.
On a night of high drama at the Pepsi Arena in Poland, the visitors took the lead through Callum McGregor before going a man down and conceding four goals before the 90 minutes was up.
Deila said their performance was just not good enough: "It was a very poor performance and worst of all was the commitment, the energy, I need much more energy in the game.
"We didn't stay together for 90 minutes."
Following McGregor's opener the Hoops proceeded to collapse, losing a brace to Miroslav Radovic, with defender Efe Ambrose red-carded a minute from the interval.
In the second-half 10-man Celtic were let off the hook when Ivica Vrdoljak missed a penalty but in the 84th minute Michal Zyro headed in number three before substitute Jakub Kosecki netted a fourth at the death to leave next week's return game at Murrayfield a pressure game for Deila, who is facing the dispiriting prospect of dropping into the Europa League.
The Celtic boss hinted that he still held onto a bit of hope that the Scottish champions still have a slight chance to turn things around.
He added: "We started well and got the first goal but then gave way to pressure and we lost our heads and started giving the ball away in midfield so many times and mistakes in the back four, some were high, some were low, instead of being together.
"But what is done is done, we have to learn from this very quick, we got the away a goal and we still have a chance.
"It is possible to win 3-0 again - like we did last year in the play-off - with the help of the supporters and we will do everything we can to do that.
"But we have to learn from this week. We need a whole different attitude and discipline in our play."
After watching his side turn in a disjointed performance, Deila vowed to make himself much clearer in his instructions ahead of the second-leg in Edinburgh.
He said: "It was not the plan to go forward at 2-1. We had a spell when we had good control but started making stupid mistakes and they got space behind us.
"That is my responsibility. I have to be much clearer as to what I expect and how we perform as a team, defensively and offensively, and tonight we lost our heads and that is not good enough."