Barcelona coach Ronald Koeman felt they were too loose in midfield for their 2-0 defeat at Atletico Madrid.
Koeman watched from the stands as his team was taken apart by a ruthless Atletico Madrid who were able to capitalise on their weaknesses.
"We can't leave that much space in behind when we lose the ball. We talked about exactly that before the game," said Koeman after the match.
"If we play with four defenders and two centre backs marking, you have to stay with your man in midfield. Nico [Gonzalez] stayed with his.
"Maybe now you understand why we've sometimes played with three centre backs."
While recognising that his team wasn't good enough at the Wanda Metropolitano, Koeman also felt they deserved more from the game.
"We deserved more but, as is almost always the way, matches are decided by moments and we didn't take our chances," said Koeman.
"For the goals, we left a lot of space and for the first we didn't mark [Thomas] Lemar.
"From midfield, you have to follow your man. That's not acceptable."
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