David Luiz admits Arsenal must improve defensively if they want to win titles.
The Gunners conceded three goals to Liverpool on Sunday in what was their first defeat of the season.
"We have to [improve]," said Luiz. "I think if you concede a lot of goals you cannot fight for the title so this is one main thing we have to think about and try to reduce and try to make the team stronger.
"It is not just about me, it is not just about the defenders, it is about the mentality of the team. I think the team already did great against Newcastle, did great against Burnley to understand the kind of game we were playing for.
"We were clinical in Newcastle with one clear opportunity. We scored and don't concede.
"With Burnley, we were clinical to understand the game. It was always to play first ball, second ball, fighting, they try to score with free kicks and things like that and we did amazing.
"[Liverpool] I think it could have been a different game if we scored [first] but we did not and this is football. Football is like that. Every week is a new history and we have to try and learn and improve our game."
