Neymar was injured while playing against Strasbourg last Wednesday in the French Cup, rolling his ankle as he fell to the ground following a couple of challenges.
PSG will travel to Manchester for the first leg of the Champions League round of 16 clash on February 12.
The rout equalled PSG's record league win: 9-0 away to Troyes in 2016, when Zlatan Ibrahimovic was the star.
Neymar was on the sidelines during PSG's 2-1 win over US Orleans in the Coupe de la Ligue round of 16.
Cavani and Neymar were both assisted by their 19-year-old teammate, with Mbappe putting on an excellent display of speed, strength and dribbling throughout the game.
Paris Saint-Germain will play Liverpool on Wednesday in their Champions League fixture at the Parc des Princes.
PSG's 12th straight win from the start of the season is a record for the top five European leagues, beating Tottenham's 11 opening wins in 1960.
Mbappe found the net just four minutes after coming on, justifying his importance in an attack which has plundered 39 goals in 11 games.
The 19-year-old star of France's World Cup title run this year, Mbappe became the youngest player to score four goals in a French league match in 45 seasons.
The Brazil star's treble included two superb free kicks, taking his tally to 10 goals in eight games overall this season.
Neymar was caught by Wylan Cyprien's flailing arm as they contested the ball near the hour mark of an otherwise one-sided contest.
Roberto Firmino scored in the 11th minute off a cross from Douglas Costa, later Neymar added a penalty kick in the 44th minute.
Fans, players and former soccer stars criticized the Brazilian for his overacting on the pitch in Russia, including a tearful moment at the end of the 2-0 win against Costa Rica.
The five-time world champions exited football's showpiece event after a 1-2 quarter-final loss to Belgium on Friday.
A debate about Neymar faking injury and overreacting to tackles is polarizing opinion between European outrage and Brazilian defence.
Ronaldo called on critics to be more objective and said referees were not providing sufficient protection for Brazil's No. 10.
Neymar had been accused of faking an injury in the game, and video of Tite's criticism was widely viewed.
The five-time World Cup champions will next face either Japan or Belgium in their seventh straight quarterfinal match, the stage they have reached at every World Cup since 1994.
The Brazilian squad and their supporters, meanwhile, have been complaining since the start of the 2018 tournament in Russia that the officials don't do enough to protect Neymar from fouls.
Philippe Coutinho scored in the first minute of stoppage time, and Neymar followed six minutes later to give Brazil a 2-0 victory over Costa Rica at the World Cup.
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