It is believed that Napoli are already trying to persuade him to sign a new contract, with agent Bruno Satin urging the Serie A side to include a release clause into his deal.
Satin added that he has already spoken to president Aurelio De Laurentiis over the future of the centre-back, while also highlighting the fact that he was not for sale.
“There’s no hurry, but Napoli want to keep him for the long-term, and settle things before the massive clubs come in,” he said.
“We’ve spoken calmly, but the president [Aurelio De Laurentiis] will decide if he wants to offer a renewal. We have contact with everyone, but he’s not for sale.”
The Senegal international has helped his team reach second on the league table, with the club also boasting the second best defensive record in the Italian top flight.
Koulibaly has already featured 35 times in all competitions for his side this term, so far managing to provide two assists in the process, but is yet to register a goal.