That is indeed a problem for Real Madrid this season, even if they field the entire main squad, the performance of the lower line and the Real Madrid midfield is still in the spotlight because it is inconsistent in its performance, especially when Ancelotti makes a lot of rotations like in the match against Leganes.
Even though Real Madrid won, Real Madrid's performance was quite bad and I didn't even highlight the defense line alone, but Real Madrid's game was not well organized in all lines so they had difficulty against a team that actually had much weaker strength than them.
The problem of defense will make the Real Madrid game not run according to the plan so that there is no good level of coordination that runs well with fellow players. Real Madrid is indeed facing problems in defense and it is quite difficult for Anceloti because almost all core players in defense cannot be played. Facing Leganes Real Madrid played less than optimal because even though they were superior, but because of inconsistent defenses made Leganes managed to equalize even though at minutes added time Garcia managed to make Real Madrid maintain victory. Now the focus on facing the derby is much bigger because if Real Madrid lose, Atletico Madrid will lead the standings so that the match must be won by Real Madrid.
Real Madrid is currently suffering a lot due to the problem of defense and they need to solve this problem very quickly. Since Real Madrid is currently at the top of the points table, but if the team loses in the next matches, then Atletico Madrid will definitely take the lead at the top. Ancelotti is very worried at the moment, he has to solve this problem, otherwise it seems that the team will go into a bad position. I think Real Madrid should be more strict at the moment and their defense needs to be made stronger. Real Madrid fails to prevent many attacks due to defense, so Real Madrid should look for a good defense at the moment.