The Anfield midfielder flourished under Benitez at Liverpool, and the Spaniard is reportedly weighing up a move for Leiva in the January transfer window.
He's not the only midfielder in his sights though, with Benitez also monitoring Atletico Madrid's Mario Suarez and Barcelona and former-Liverpool star Javier Mascherano.
The Napoli boss is looking to strengthen his midfield, and Leiva presents an attractive option because the Brazilian has not played Champions League football.
He would not be cup-tied for the second half of the season, with Atletico Madrid well-placed to qualify for the knock-out rounds following their 3-0 victory over Austria Vienna on Tuesday evening.
Leiva, who has 22 caps for Brazil and is hoping to travel to the World Cup on home soil, has made over 220 league appearances for Liverpool since his 2007 switch from Gremio.
The 26-year-old is a fan favourite at Anfield, and with Steven Gerrard flourishing in a more withdrawn role this term, Leiva and the England captain have proved an effective duo in the middle of the Liverpool midfield.
But Benitez has already persuaded one Reds star to join him in Italy - Pepe Reina joined the Serie A club on loan over the summer.