Chelsea boss Thomas Tuchel admits they're working on fixing their defensive problems.
While acknowledging there can be a difference in how players approach games in different competitions and different situations, Tuchel will not accept any drop off in effort, and says it is up to him push the squad to be as ready as possible in any situation.
"It's human to be tired, it's human to be a bit more alert if it's a knockout game than in a normal match," he said.
"It's okay to feel less tension before a normal match in the Premier League than if you go to the Bernabeu. It's normal because it's maybe less tension and it's less excitement and it's less pressure, but it cannot lead to having less investment. This can never happen. We cannot run more against Madrid or have more sprints or more effort."
However the boss is satisfied that when a drop off in application occurred in the Brentford and Real Madrid games at the Bridge, it was addressed suitably, as seen by the three performances and results that followed and the data on physical performance that was studied. He does not think those previous failings at home reoccurred in the same way against Arsenal.
"That's why it's tough to really understand the reason why," he admits, before explaining one defensive shortcoming.
"It's a mix of big individual error and a lack of commitment in one-on-one defending and we have proof for it and the players know it and see it.
"We have to defend with more consequence in and around the box. You can do it to a certain point with structure and with closing spaces, but you arrive in the last 20 metres at a moment where you need to take care about your individual challenge. We were not good enough in the game against Arsenal to do this.
"Okay, there are also reasons for it. We had to change in the back three, we had some changes in the formation, but still we can do better, we should do better."
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