Kalidou Koulibaly is the best centre-back in the world and is worth €150million, according to Napoli head coach Carlo Ancelotti.
The 27-year-old has been at the Stadio San Paolo since signing from Genk in 2014, developing a reputation as one of Serie A's top defenders.
Senegal international Koulibaly has been linked with a move to Manchester United but Ancelotti warned off potential suitors.
"The best centre-back in the world? I would say so," he told Tuttosport. "And he can still improve. He is worth €150m and he is not available for transfer.
"Koulibaly’s contract expires in 2023, in 2021 there's a €150m clause but Napoli do not need to sell, the president [Aurelio De Laurentiis] does not want to sell and the question doesn't come up."
Napoli are set to finish second in Serie A for a second straight year, with Juventus holding a 17-point lead with six games to play, and Ancelotti claims he is happy to be runners-up.
Ecco la classifica aggiornata dopo il recupero della 25ª giornata! pic.twitter.com/r09oKYS78f— Lega Serie A (@SerieA) April 18, 2019
"Second place is not a discredit to us, it’s a credit to Juventus, who are going along at an exceptional pace," added the former Chelsea and Real Madrid coach.
"If they [Juve] continue like this, they can finish with 100 points."
Napoli was Ancelotti’s first coaching job in Italy since leaving AC Milan in 2009 and the 59-year-old is satisfied with the decision he made.
"Returning to Italy after nine years, I could not have made a better choice than Napoli," he added.
"When a new coach arrives at the team, many things change. If we are going to break Juventus’ dominance we will need a collective effort.
"The other rivals must also be strengthened if we are to become more competitive."
Napoli host Arsenal on Thursday seeking to overturn a 2-0 first-leg loss in the quarter-finals of the Europa League.