Ange Postecoglou admitted Celtic have to improve sharpish and told his despondent players to use their Bayer Leverkusen thrashing to "fuel some fire" to turn things around.
The Hoops boss watched his side ship another four goals as they slumped to a second successive Europa League group stage defeat.
It’s now just two wins from eight games for the Aussie who takes his side for a huge Pittodrie pressure game against Aberdeen on Sunday.
Postecoglou was visibly gutted as spoke after the Parkhead pummelling at the hands of the German giants.
Celtic missed some gilt-edged chances and met an opposition goalkeeper in inspired form but Postecoglou knows there is no room for excuses as a sell-out crowd was let down.
He admitted: “We have to get better soon. We've had a number of injuries, we rebuilt the squad, and it's taken time, but we can be better.
“We have just got to persevere, push through it and use the disappointment to fuel some fire to turn things around
“We are very disappointed in the dressing room and we should be and we have to have a reaction.
“We’ve made things difficult for ourselves in the group. Towards the end there was no need to concede a fourth.
“It shouldn’t have been a 4-0 game and we have to be stronger mentally towards the end of the game and keep ourselves in the game.
“I’m disappointed for our fans. They created a great atmosphere and we got such a great start to the game.
"We had some great chances but they’re a good side. They were clinical in the box, we were wasteful and made mistakes you can’t make at this level.”
Postecoglou welcomed back Kyogo Furuhashi and Callum McGregor from injury with the former missing a couple of glorious opportunities.
That could have been down to a lack of match sharpness but Postecoglou said: "The keeper pulled off some unbelievable saves but it was good to have Kyogo and Callum both back in the team because it makes a difference - but not enough.”
