Celtic legend Pat Bonner has criticised Bhoys defender Jozo Simunovic for his mistake at Celtic Park which let FC Copenhagen score the first goal of their 3-1 win in Glasgow.
With the first leg of the Europa League last 32 tie having ended 1-1 in Denmark, Celtic started Thursday evening as firm favourites to progress to the last 16.
Celtic fell behind at Celtic Park in the 51st minute, but managed to draw level through an Odsonne Edouard penalty with seven minutes left.
FC Copenhagen hit back however as Pep Biel struck in the 85th minute, while Celtic were finished off when Dame N'Doye scored in the 88th minute.
Celtic have now exited the Europa League 4-2 on aggregate and Bonner has no doubt the rot was started by a mistake from Bhoys defender Simunovic.
"The first goal was key for me", Bonner said on BBC Sportsound.
"Jozo Simunovic lets the ball bounce and run down the side of him when he should have been booting it into the stands.
"I've seen Simunovic make that mistake so many times", the former goalkeeper added.
Bonner also expressed disbelief at the quality of defending Celtic served up throughout the evening in Glasgow.
"I can't believe the defending I've watched here tonight from Celtic.
"That's been three goals they've given away and it's all of their own doing", he added.
Celtic will now switch their attention back to domestic matters as they look to seal another treble of trophies, with their European ambitions on hold until next season.
