#4 Kalidou Koulibaly
Real Madrid have not been able to fill the void in their defence after Pepe left. With 32-year-old Ramos and injury prone Varane, Real Madrid could definitely use Napoli's Koulibaly. Koulibaly has been a beast for Napoli and he is also one of the best defenders in the Serie A. He is 27 years old which means that he has enough experience to play for Real Madrid every week and also has 5 years of his prime left.
With rumours of Antonio Conte becoming Los Blanco's next coach, Koulibaly will be the perfect player to play in a three-man defence with Ramos and Varane.
Even if Conte doesn't join Real, they should pursue Koulibaly as a world-class team like Real Madrid should have three world-class centre-backs. With Vallejo who spends most of his time injured and Nacho who has to cover up for all the defensive positions, Koulibaly would be a good find for the struggling club.