Chelsea have made formal their interest in Kalidou Koulibaly by lodging a big-money bid with Napoli.

The Telegraph reports that the Blues have submitted an offer worth £34million for the 25-year-old as they continue their summer search for a quality centre-back.

Chelsea have been linked with the French-born Senegal international for some time and have now made a move to lure him to Stamford Bridge.

Incoming Blues boss Antonio Conte wants Koulibaly's strength in defence and ball-playing ability when going forward and is prepared to pay £31.5m up front, with a further £2.5m in bonuses.

Chelsea have also been linked with Juventus star Leonardo Bonucci but it is believed that the West Londoners are more confident of landing Koulibaly.