And Ter Stegen, who made several key stops as the Catalans moved three points clear in Group F, did not hold back in the aftermath.
"It is necessary to talk about some things," he told Movistar Plus. "We have to do it between ourselves, I will not say it here, but there are things to improve - a few of them.
"This is an internal matter as well, I don't want to do it here. I would like to talk to those who were on the field first.
Barcelona, Slavia, Champions
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"They scored against us right on the first chance of the second half. This can't happen to us, I was quite alone.
“He doesn't do anything special, he takes a pass and it's just ahead of the goal. We have things to improve, that's a tactical thing that we didn't go back to 100 per cent. That's it, things that happen during a game.
"On a personal level I always want to be there. If I can help the team, even better. In the first half we had chances against us in which we were not well placed but these are things that happen.
Barcelona are top of La Liga with 19 points from nine matches, one clear of Real Madrid.
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