The Premier League giants were beaten 3-2 in Turkey against Galatasaray on Thursday night.
Two first half Victor Osimhen goals proved decisive for the Turkish team in this contest.
Post-game, Postecoglou stated: “No I don’t think so. It was probably a combination of all those things. I just felt it was self-inflicted. We had real simple solutions out there to keep the ball and as we showed with 10 men it wasn’t that difficult to do. We just didn’t.
“Individuals within needed that to be stronger on the ball and make sure we play the kind of football we try to do every week and we didn't do that. Maybe it was a little bit the changes I made and the environment or the atmosphere or whatever you want to call it, the opposition. The moments that stick out to me are when there was no pressure on us and we are still giving the ball away.
“I think we need to be better in those moments because if we are better in those moments then you minimise the threat the opposition has but also we get a foothold in the game in the areas we want to. We did it with 10 men. We were playing through them quite easily with 10 men but with 11 we just didn’t have anywhere near the conviction we needed to so it’s disappointing.”