Former Chelsea manager Rafael Benitez has admitted Kalidou Koulibaly must improve his concentration levels ahead of playing for the Blues.
The defender has completed a £34million switch to Chelsea from Napoli and is expected to fill the void left by Antonio Rudiger, who has joined Real Madrid on a free transfer.
But 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'.
These worries have left the former Blues manager doubting whether the 31-year-old will be as dominant as he was in Serie A.