#3 Bring experienced backup players to the squad
When Zidane sanctioned the sales of Pepe, James Rodriguez (on loan to Bayern Munich), Mariano Diaz, Alvaro Morata, and Fabio Coentrao before the start of last season, he lost something valuable apart from the individual talent that each of the aforementioned players possesses: valuable experience.
In the 2016/17 title-winning season, a strong factor that helped Real Madrid in winning La Liga was the fact that they had a very strong bench to call upon from when needed. This gave Zidane the liberty to rotate his squad before each Champions League match and give his main players a rest while the others got a run out and got the job done.
These backup players had a huge hand in winning the trophy, with the likes of Morata and James chipping in with goals and assists when needed. The presence of Pepe, Nacho, and Coentrao allowed Ramos, Marcelo, Varane, and Carvajal to rest before big matches in the Champions League.
A number of young players were brought in to replace the group of players that left, but they lacked the experience of changing games on their own despite possessing the quality.
If Zidane is to keep up with his policy of rotating the squad in the league, he needs to bring in experienced backups to his star players, be it due to injury or when he wants to rest them.