Koeman was left unimpressed with Barcelona’s schoolboy defending at the Estadio Ramon de Carranza.
Striker Alvaro Gimenez put the hosts in front eight minutes into the game and the Catalans could not do enough to equalize throughout the first half despite having the lion’s share of the possession.
Barcelona finally found the equalizer twelve minutes after the interval through an own goal from Pedro Alcala but the hosts restored their lead six minutes later thanks to Alvaro Negredo, who benefitted from a poor defensive mixup between Clement Lenglet and keeper Marc-Andre ter Stegen.
“The defeat is difficult to explain. We came from good games. The first half has not been good. And in the second we have been better, but it is incredible that we have lost due to a mistake that is not expected from our team,” Koeman told Marca after the game.
“You cannot fit in. a goal on that serve. It's from not being focused. The attitude hasn't been good tonight. Not just from the defenders.”
"It is very difficult to explain some of the goals we have conceded. I think they may be due to lack of concentration. We lack aggressiveness without the ball. That may be the issue of conceding goals. It is not easy to explain how we have conceded the second goal."
Koeman added: "It is a giant step backwards in our chances of fighting for LaLiga. It is disappointing, but we have to accept it. A distance of 12 points to a team as strong as Atlético de Madrid is a lot. There are still games to play, but if we do not improve our attitude and our ups and downs away from home, we can't say anything more.”
