Celtic's problems at the start of this SPFL season stem from the situation at the back, according to Scottish football journalist Robert Grieve.
Neil Lennon is under increasing pressure with Celtic six points behind Rangers, albeit with a game in hand.
Celtic
"Defensively, they have not been good enough. The goals that they have conceded have not been good enough.
"If you look at the Rangers game, the overall performance was so lacklustre in an Old Firm that was going to mean a lot to both teams. There were no fans and that seemed to seep into the players' performances.
"The three goals against Aberdeen at Pittodrie on Sunday; they were very poor goals. In the AC Milan game, we would think of them to be a top team but the goals they conceded were poor."
Celtic's marquee signing for the summer does not get off scot-free, either.
"Shane Duffy was exceptional in his first few games, he scored in his first two games - at that point, you're thinking it is a great signing.
"Defensively, he hasn't looked very clever. I was there the day that he was unveiled, and he described himself as a no-nonsense centre-half: head it, kick it, get the ball away.
"He has not done that."
Grieve believes that Duffy's performances may be down, in part, to a dental issue mentioned by Neil Lennon.
"I don't think that he is in great shape that way but if you ask Shane Duffy himself, I think that he would admit that he would admit that his performances have been pretty since coming to Celtic."
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