The Partenopei have formalized their interest in the 23-year-old but the Ligue 1 outfit is holding out for more money.
Olympique de Marseille has turned down an offer in excess of 12 million euros from Napoli for defender Nicolas N'Koulou, president Vincent Labrune has revealed.
The Partenopei had been linked with a move for the 23-year-old since the back end of 2013 and have now returned with another bid for the Cameroon international.
However, the Ligue 1 club is reluctant to allow one of its most prized assets to depart the Stade Velodrome for the money on offer.
Speaking to RMC, Labrune said: "We had an offer from Napoli in mid-December, which was for more than 12 million euros, and was not acted upon. There is little chance of him going."
N'Koulou has been an ever-present in the league for Marseille this term and he also started five matches of the club's unsuccessful bid to progress from the Champions League group stages.