The Campanian club are bidding to join Juventus at the top of the table with victory at the Stadio Olimpico, should the Bianconeri lose at home to Fiorentina earlier in the evening.
A Napoli win would also pull Walter Mazzarri's men nine points clear of third-placed Lazio but Cannavaro knows taking all three points in the capital will be no mean feat.
He told sscnapoli.it: "Tomorrow [Saturday] will be the toughest challenge we've faced so far.
"Lazio are one of the trickiest opponents to beat and especially when they're at home. They have a great team that rises to the occasion for the big matches.
"We may have won the reverse fixture but on the whole they are having a great season and are flying high in the table. It should be a great match but a very difficult one."
Star striker Edinson Cavani will be key to unlocking the Biancocelesti defence and Cannavaro believes the Uruguayan is ready to commit his future to the San Paolo despite strong interest from abroad.
"Cavani has scored nearly 100 goals for Napoli in two and a half years and so it's clear why there are lot of clubs chasing such a great player," Cannavaro added.
"That kind of attention is good and well-deserved but Edi just wants to give his all for Napoli and the blue shirt."
Wing-back Christian Maggio faces a late fitness test but midfielder Blerim Dzemaili has stayed behind having picked up a one-match ban.
The focal point of Lazio's attack, Miroslav Klose, will not feature after suffering a leg injury that will sideline him for up to eight weeks.
Former Manchester United and France striker Louis Saha has subsequently been drafted in as cover following his release by Sunderland and the 34-year-old is raring to go.
He said: "I'm really happy to have joined this great club and to have accepted this opportunity.
"I've found a great group of lads and working with them will be a pleasure. I want to do my best so we can win as much as possible.
"I'm here to help in the absence of a top player like Klose and I will do so gladly.
"Am I ready for Napoli? I know it will be a difficult game but I want to give my all to help the team."
Injured trio Ederson, Cristian Brocchi and Hernanes add to head coach Vladimir Petkovic's problems but the Bosnian has no suspensions to contend with.