Koulibaly is yet to sign a new contract with his current club, but Napoli want to keep the defender and are not looking to sell.
According to reports, the only way in which Napoli will sell Koulibaly is if they can sign Torino defender Nikola Maksimovic.
Chelsea have made a number of bids for the Senegal international, but have so far failed in all of their attempts to sign the player.
It is thought that Chelsea themselves may be interested in Napoli transfer target Maksimovic, and may start a bidding war with the Italian club.