Kalidou Koulibaly has reportedly agreed a new contract with Napoli to June 2023 that has no release clause.
The Senegal international centre-back is currently tied to the club until June 2021.
According to the Corriere dello Sport, the improved deal would bump his salary up to €3.5m per year.
Crucially, there would be no release clause included, meaning any club that wanted Koulibaly would have to negotiate directly with Napoli.
The 27-year-old defender joined the club from KRC Genk for €7.75m in the summer of 2014.
His value on the transfer market is now believed to be around €90m.