Celtic skipper Scott Brown described the second half of their 7-0 thrashing by Barcelona at the Nou Camp as unacceptable.
The Hoops were losing 2-0 at the interval through a Lionel Messi double, but Moussa Dembele had a penalty saved by Marc-Andre ter Stegen when it was 1-0 for the home side.
However, the Scottish champions capitulated after the break and Messi added a third for his hat-trick, Luis Suarez a double with further goals from Neymar and substitute Andres Iniesta.
It was Celtic’s heaviest European defeat and Brown was not happy.
He told broadcasting media: “Everyone in that changing room was disappointed. It was a heavy, heavy defeat.
“I think in the first half we had a penalty and I know we miss it but that’s football, but it is the second half that is really disappointing.
“To lose five goals in 45 minutes is unacceptable.
“We didn’t do well enough on the ball, they kept giving it back and they are entitled to score, they are a great team. But we should do better than that.
“It is hard to take but yet again, they are a great team but we need to bounce back.
“We have Man City the next game, and we need to take something at Celtic Park, and with our fans anything can happen.”
The Parkhead midfielder is looking to take some lessons from the Barca defeat, put it on the back burner and and get back on track in the league against Inverness on Sunday.
He said: “They are the best team in the world, there is no doubt in that.
“But we need to defend better from the front middle and back, be more compact and brave on the ball and even here we usually do better than that.
“We have another big game on Sunday against Inverness and we need to keep our run in the league going, keep our 100 per cent run going and we will focus on the Champions League when it comes around again.”