Postecoglou’s side slipped to a 3-1 loss at Leipzig in the Champions League which leaves them with just a single point following three group stage matches.
The game was level at 1-1 until the 64th minute, when a Joe Hart error handed the ball to Dominik Szoboszlai, who fed Andre Silva, who then struck to make it 2-1 to the hosts.
Silva scored his second of the game and Leipzig’s third with 13 minutes left to end any Celtic hopes of claiming a point.
Celtic legend Bonner thinks it was clear to see that Postecoglou was angry when Celtic conceded for the second time, but admits he will never hang his players out to dry in public.
Bonner said on BBC Sportsound: “Ange Postecoglou is a father figure.
“He isn’t going to come out and slate the players, but you could see on the sidelines he was really angry with the second goal.”
The former Bhoys star also admitted that Celtic have to improve their pressing at Champions League level, with more organisation needed.
“When you go up a level, your press has got to be more organised.
“That’s the bit of learning I think Celtic have to do.”
Celtic next have a meeting with St Johnstone on the agenda in the Scottish Premiership, while then Leipzig are due to visit Celtic Park in the Champions League.
