Napoli have been working on signing various players to contract extensions as they try to better secure the core of their team for the next few years, Kalidou Koulibaly among them. Just because a player signs a new contract doesn't mean that other teams won't come sniffing around, though, so they need to find a way to discourage other teams as they can -- and for Napoli and Aurelio de Laurentiis, that discouragement comes in the form of big ol' release clauses.
We've seen Napoli stick to their release clause for Gonzalo Higuain time and again whenever rumors around him pop up, and apparently they want to employ the same mechanic for Kalidou Koulibaly if they can get him to agree to an extension. According to reports, they want to insert a €40 million release clause into his contract, which would be an effective deterrent to many offers.
It's not an amount that would keep the truly megarich clubs from going after him, but whether or not Koulibaly is good enough to truly warrant their attention yet is debatable. If they do, though, Napoli would have a healthy amount of money in their pockets with which to replace him, and non-megarich teams would probably steer clear of him for now.
The contract offer would also reportedly double Koulibaly's wages from €800,000 per year to €1.6 million, something he's easily earned since joining Napoli two years ago. He made an immediate impact in the side after joining, far bigger than was expected or even hoped that soon, and has improved by leaps and bounds since then. Heck, if anything he's earned an even bigger raise than that.
The sky is the limit for Koulibaly's career at this point. Napoli are doing all they can to make sure that he's with the team for the long run, and it's hard to argue with what they're reported to be trying. Please, Kalidou, sign the papers.