Well, when he says that then he knows what he is talking about. I think Ancelotti is aware about how long it will takes for his injured players to come back to training and to the fields and he knows that he has other temporary options. Additionally getting another defender, means more money to spend for a player to stay in the benches. I think Ancelotti needs to focus more on an attacker and maybe midfield for the long term. For short terms, he might get a defender with a short loan contract rather than signing him a couple of years one?
Real Madrid are currently transitioning to regenerate their players and for now it is going quite well. By combining senior players and young players it is a very wise decision taken by Real Madrid.