Sergio Busquets blamed individual errors for Barcelona's 2-1 defeat at Cadiz, with Oscar Mingueza, Jordi Alba and Clement Lenglet all contributing to the home team's win.
Barça midfielder Busquets said that "we reacted well after the first goal but when it's two goals it's even more difficult. We created chances, got forward and then equalise. But just as it seems we have a chance, we make another mistake and it's even more difficult."
He added: "I think individual mistakes have cost us a lot of points and today to concede so early, we can't give that advantage to the opposition. We also need some fortune but have to keep going, there's nothing else for it."
Asked why Barça are so different in the Champions League and the league, he said: "It's true, we seem another team in the Champions League... I don't know why. If we had the answer, this probably wouldn't happen.
"What I can say is that in recent games, mistakes have marked the outcome. And once we're behind, it enables teams to shut up at the back, deny us space. It's not to do with the attitude or the commitment of the team. But starting games like this makes it much more difficult."
Busquets finished by saying: "It's worrying to lose so many games. The more we slip up, the further we are away from the top, which is where we want to be."