Aurelio De Laurentiis has confirmed Dries Mertens has signed a new deal with Napoli and says his release clause ensures there will be no repeat of the deal which saw them lose Gonzalo Higuain to Juventus.
The Serie A side wanted to hold on to their star attacker, but were forced to sell him to their rivals when they triggered his release clause with a €90 million offer.
While Mertens has been linked with a move away from Napoli after an excellent season, a new contract which keeps him at the Stadio San Paolo until 2020 has been confirmed and the president says it includes a clause that means he can only leave for a foreign club.
"From 14:30 pm on Friday until 1.40 am Saturday, we were on the phone with Mertens' lawers and counselors," he told Radio Kiss Kiss Napoli . "Together with my tax experts, after many hours of technical discussion, we developed a perfect bilateral relationship for Dries and Napoli that protects the fans and me.
"Mertens will remain with us for several years, unless he wants to go to China if someone were to exercise the clause that he wanted, even if I am not in favour of them after Higuain's departure.
"In life you have to learn. Experience shows, no one is born a professor. The new clause can only be exercised by a foreign team. In Italy, Mertens will play only for Napoli.
"We are setting up a war machine, we can no longer lose points to smaller teams."
While Napoli are at least sure of a place in the qualifying rounds of next season's Champions League, they can finish second and book a spot in the group stages if they beat Sampdoria and Roma lose to Genoa on the final week of the campaign.
Although they may not match last year's runner-up spot, they have collected more points with a game to spare, and De Laurentiis took the time to praise coach Maurizio Sarri for his work.
"He has made incredible progress and each time, proving to be educated and intelligent," he said. "He puts his experience to good use and this is the biggest guarantee. His mistakes will not be repeated.
"I am delighted that he is with us "