Team like Real Madrid should have good players or worldclass players in their bench as backup for such situation when injuries are coming to affect the starting eleven players, but they literary don't that enough quality players in their bench which is why some of their fans are already making that as an excuse in case if they lose their match against Barcelona.
If someone come and say that Madrid don't have squad depth, their fans will come for that person, and it is a plain truth they need to believe in; moreover, their defense is not as strong as they may expect which is why they are looking for possible solutions before the January transfer windows; but if they continue like this, they will definitely suffer at some points because some players will surely get injured.
Madrid has good players who can replace injured or suspended players. In the case of Daniel Carvajal who suffered a knee injury and might return in July next year, there is a qualified replacement. The Spanish defender Lucas Vazquez is an experienced player that can cover up for the left-back position until Daniel recovers.
However, the club management and coach Ancelotti will not relax because anything that happens to Lucas, such as injury or suspension, will have a negative effect on the club's performance. They will be forced to depend on versatile players who can be used in different positions. To reduce the risk they will have to get another player that can serve as a backup. It is important to state that clubs like Madrid will always be for the best; this is why they will push hard in the January transfer opening to get quality players.