Hysaj was believed to be on the radar of Arsenal and Chelsea in the summer, but a move never materialised.
The Albania international joined the Partenopei in 2015 from Empoli on a six-year deal, but agent Mario Giuffredi believes that the 23-year-old is destined for even greater things.
"He decided to stay at Napoli because he had started this project with Maurizio Sarri and all together they believe this can be the year of the Scudetto.
"Hysaj wanted to continue the work they had begun, then in June we'll see what to do."
Hysaj has made 94 appearances in all competitions for Napoli.