The striker was the subject of two offers from Everton over the summer.
"We met shortly after the end of the transfer window," agent Silvio Pagliari confirmed on TMW Radio.
“We're close and we're settling the final details. Napoli want to invest in Manolo, and we're happy about the 'no' to the offers which came in for him this summer, albeit they were very important ones.
“He's positive, I heard from him this morning and he's fired-up ahead of the return of the League and the Champions League.
“He knows this is an important season and Napoli can be protagonists.
“When [Gonzalo] Higuain left [for Juventus] I was almost sure he [Gabbiadini] would stay, it's hard to replace a player like Manolo after you've already lost Higuain.
“The Argentinian didn't think he'd leave, nor imagined such an effort on Juve's part."