Former Chelsea boss Rafa Benitez says Kalidou Koulibaly still has some rough edges in his game after completing his move to Stamford Bridge.

Benitez, who managed Koulibaly during his time as Napoli boss, has shared his concerns over the defender losing focus on the pitch and his tendency to be "overconfident".

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.

"Powered by '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."

Benitez has also suggested that while Koulibaly's aerial ability was not the best, he was always willing to try and improve and take on advice from the coaches.

"Aerial ability wasn't his biggest strength but in Italy, that mattered a bit less and he was ok," he said.

"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."