As failings go, this was a seismic one by Celtic and in analysing who is at fault, there is a world of criticism for everybody.

This was a defeat for the collective - players, manager, board. They are all in the frame together. It was an illustration of a club gambling on progress by waiting for Champions League qualification to be secured before properly refreshing its squad.

It is a thunderous example of how they have allowed their standards to drop, on the pitch and off it. Not that many months ago, Celtic went toe to toe over two legs with the Bayern Munich of Manuel Neuer, Dayot Upamecano, Joshua Kimmich, Jamal Musiala, Harry Kane, Kingsley Coman and Thomas Muller.

In losing 3-2 on aggregate and coming within seconds of taking the Germans to extra time in their own backyard, Celtic had momentum, something to build on.

They also had a stack of money in the bank and a support, broadly, facing in the same direction as the board. There was relative harmony and positivity. A rare commodity in Glasgow.

Now there's bitterness and rancour. They have blown their feelgood factor sky high.