Chelsea had signed Kalidou Koulibaly from Napoli on a four years contract to replace Rudiger, the guy is a very solid and quality defender who will compliment Tiago Silva at Chelsea backline he is a perfect replacement, though he is 31 he is playing at the top level and one of the best centre back in Europe that is why he was signed for a four years contract despite being 31 while Tiago is 37, I believe the duo has the needed experience to assist Chelsea in their defence, hopefully he will settle down and adapt quickly before the commencement of the premier league in August 5.
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https://www.bbc.com/sport/football/62168549Chelsea main hunt is De Ligt, but the agreement between the two parties is very complicated so far, especially since Bayern Munich has interfered in this transfer because Bayern Munich offer is bigger than Chelsea offer. Perhaps from this Chelsea turned their attention to Kalidou Koulibaly who seems to be the most appropriate solution for their defense next season. I think Tuchel besides getting Kalidou Koulibaly he will also monitor the developments that happen to De ligt. he really wants to get De ligt.
De Ligt's price was too expensive and negotiations with Juventus did not end until finally Chelsea chose to bring in Koulibaly from Napoli, Koulibaly's quality is very good and he is much more experienced. And after signing Koulibaly I think Chelsea will stop chasing De Ligt. because the position of the two players is the same and it is impossible for Chelsea to bring in both of them for one of them to fill the bench because both are quality players.