Sarri missed Juventus' home game against Napoli with pneumonia in August and Sunday's game at the Stadio San Paolo will be his first since leaving the club in 2018 before his move to Chelsea.
"It will be a tremendously difficult game, emotionally it will be particularly special. My relationship with Naples and above all the city was strong," said Sarri, after Juve reached the Italian Cup semi-finals with a 3-1 win over Roma on Wednesday.
Juventus are top of the league with a four-point lead on second-placed Inter Milan, but Napoli -- Serie A runners-up in the past two seasons -- are struggling in 11th position, 14 points off the Champions League places.
"We must not look at their position in the table," Sarri continued. "They have a strong team. They are going through a difficult time but have good players.
"There are three points at stake."
Napoli lost 4-3 in the reverse fixture this season.
But the team are a shadow of the eye-catching side Sarri left in May 2018 to be replaced by Carlos Ancelotti.
Ancelotti helped the team maintain their runners-up position last campaign but was replaced at the troubled side by Gennaro Gattuso last month.
Gattuso has lost four of his five Serie A games in charge and the club have not won at home in the league since October 19.
But they have been boosted by booking their ticket to the Italian Cup semi-finals with a 1-0 win over in-form Lazio this week.
"We played with hunger, character and the right spirit, showing real grit, something we had been lacking up till now," said Gattuso.
"Now of course we need to keep it up, to climb back up the table."
Second-placed Inter Milan are at home against sixth-placed Cagliari this weekend, after their title bid was stalled with back-to-back draws.
Lazio -- on a club record 11-match league winning streak -- are third, six points behind Juventus with a game in hand, and two adrift of Inter ahead of the Rome derby.
Paulo Fonseca's Roma are seven points behind their city rivals in the final Champions League berth.
The teams played out a 1-1 draw in the reverse fixture in September, and last season had a win each.
Simone Inzaghi's Lazio are pushing for a first Scudetto since 2000, after crashing out of the Italian Cup, which they won last season.
Flagging Atalanta, in fifth, travel to Torino, while Zlatan Ibrahimovic's eighth-placed AC Milan visit Brescia on Friday looking to edge closer to the Europa League places.
Brescia striker Mario Balotelli will miss the game against his former club after being handed a two-match ban for arguing with the referee last weekend.
One to watch
Atalanta's Duvan Zapata is desperate to end his three-match goal drought since returning from injury.
The 28-year-old scored six league goals in seven games before being sidelined for three months with a thigh injury.
It is the former Sampdoria forward's longest stretch without scoring since his first goal for Atalanta back in November 2018.
50 - Atalanta's league goals scored in 20 games
27 - Napoli's points deficit to Juventus
23 - Ciro Immobile's league goals for Lazio this season
12 - Ronaldo's goals in last eight games
3 - Maurizio Sarri's seasons as Napoli coach
Fixtures (all times GMT)
Brescia v AC Milan (1945)
SPAL v Bologna (1400), Fiorentina v Genoa (1700), Torino v Atalanta (1945)
Inter Milan v Cagliari (1130), Hellas Verona v Lecce, Parma v Udinese, Sampdoria v Sassuolo (1400), Roma v Lazio (1700), Napoli v Juventus (1945)