Benitez flags major concerns regarding Chelsea's transfer for Koulibaly

Rafael Benitez has revealed that Kalidou Koulibaly must improve his concentration if he is to succeed in the Premier League after the 31-year-old made the switch to Chelsea.

The Blues confirmed that the Senegal international has joined the club from Napoli for a fee in the region of £34m on Saturday morning, becoming their second signing of the transfer window. This is after Raheem Sterling made the big-money move from Manchester City earlier in the week.

Koulibaly is an experienced centre-back, who made more than 300 appearances for Napoli during his eight-year spell in Italy. He has been named in the Serie A Team of the Year on four separate occasions and also lifted the Africa Cup of Nations with Senegal back in February after they beat Egypt in the final.

Thomas Tuchel has been chasing the defender all summer and has now finally got his man - three weeks before their Premier League opener against Everton. However, Benitez, who worked with Koulibaly throughout his time in Naples, has warned the Blues of a number of flaws in his game - comparing him to Antonio Rudiger.

He told The Athletic: "He must improve his concentration at times. He can be guilty of losing focus and can be overconfident, but he has been hugely influential at Napoli and people I know and trust have told me that he has been the best centre-back in Italy during this time.

"This season will be the Premier League for him and he could be fine for the way that Tuchel wants to play. He has similarities with Rudiger - he is very good at running with the ball, he's good with both feet.

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"Is he a little bit too nice? We will see what happens at Chelsea. As I said, in Italy he was fine because he was so quick, but I doubt he will be so dominant over here.

"Aerial ability wasn't his biggest strength but in Italy, that mattered a bit less and he was ok. It will be interesting to see how that develops in the Premier League but he was always very keen to learn. He spent time with me and my staff after training sessions to work on his heading and improving his technique."

Chelsea were in desperate need of adding another central defender to their squad after Rudiger joined Real Madrid on a free transfer, while Andreas Christiansen left the club to join Barcelona. Meanwhile, Cesar Azpilicueta is expected to join the latter in making the switch to the Catalan giants.