The Polish international has become a key figure at the Stadio San Paolo, and as a result negotiations over an improved deal have been ongoing for months.
Il Corriere del Mezzogiorno reports the two sides have all but agreed on a deal that will see Zielinski earn €4m a season until 2025.
The midfielder’s entourage were able to secure a sizeable pay increase – double what he currently earns – because Napoli were adamant on including a release clause in the contract that is believed to be worth €100m.
The Azzurri hope that figure will be enough to ward off potential suitors, as the likes of Liverpool and Inter have been linked with a move for the 25-year-old in recent months.
So far this season the midfielder has two goals in 35 appearances in all competitions.