Celtic coach Ange Postecoglou said a crucial goalkeeping error in his team's 3-1 Champions League loss at RB Leipzig happened because they tried to "play it safe".

With the score locked at 1-1, former Manchester City goalkeeper Joe Hart passed the ball directly to Leipzig midfielder Dominik Szoboszlai, who teed up Andre Silva to put Leipzig in the lead.

When asked at the post-match press conference if Hart had apologised to teammates for his error, the Australian coach snapped back "that's not how football works, mate."

Postecoglou said he "could see the mistake coming" after his team looked to settle for a draw, rather than push for the win.

"It's not about the mistake, it's about beforehand. We had a lot of the ball but we were just passing it back.

"You're doing what you think is safe, but really it's not.

"It was creeping in before that, after we scored, we almost wanted to settle for that and we kept passing the ball back to him.

"If it wasn't Joe making the mistake it would be someone else."

Postecoglou said his team "lost their endeavour" and fell into "survival mode".

"When you're coming away from home in a game like this, where you've fought so hard and you're clawing your way back into it - you need to stay in that positive mindset and make (the opposition) uncomfortable."

The win was Leipzig's first this campaign and they sit third with three points after three matches.

Celtic, who will take on the German side in the return fixture in Glasgow next week, are last with one point from three games.