Naples radio station Radio Kiss Kiss, as quoted by the Daily Mirror, is reporting that Napoli have placed a huge price tag on the Senegal international ahead of the summer.
The same article states that Arsenal and Manchester United are heading up interest in the Napoli defender as the Premier League rivals look to improve their squad.
According to the same story, Napoli director of sport Cristiano Giuntoli will only consider a massive offer for the 26-year-old defender.
Koulibaly scored five goals and made one assist in 34 appearances in Serie A this season to help Napoli to challenge for the Italian top-flight crown.
The African defender scored a sensational winner in a 1-0 victory over Juventus in Turin last month to give the Naples outfit hope of overhauling the defending champions.
Koulibaly moved to Napoli from KRC Genk in a €7.75m deal in the 2014 summer transfer window.
The Italian side finished in second place in the Serie A table this term to miss out on a first Italian top-flight crown since 1990.
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