The 35 year-old's current deal expires this month.
Mertens said, "I want to make the right choice. I want to find a good club. I'm calm, but I think a lot about my choice.
"I thought I'd stay at Napoli, it's strange that they waited so long.
“Regarding the contract extension at Napoli, I haven't heard from anyone yet. I hope in the coming days or weeks to let you know."