The Brazilian centre-back will arrive in São Paulo on Monday to complete his medical and be presented by his new club.
Napoli have confirmed the deal on their official website although Santos have yet to comment.
The loan deal is expected to run until the end of 2014 with the Peixe required to pay only the salary of the player – thought to be approximately £25,000 a month.
The 22-year-old came through the ranks at São Paulo before spending relatively unsuccessful periods with Tottenham, Siena and Napoli.
