Cavani joined United on a free transfer in October following the expiration of his contract with PSG, which led him to miss the final three rounds of last season's Champions League.
The Uruguay international, who trained with his new team-mates for the first time on Sunday, is PSG's all-time record goalscorer having found the net 200 times during his seven years with the club.
PSG could face Cavani on Tuesday when they welcome United to the Parc des Princes for their 2020-21 Champions League opener.
"Il est dans une autre équipe maintenant. Je lui souhaite le meilleur, mais il ne fait plus partie des nôtres. On va jouer contre lui, et on va essayer de les battre"— Téléfoot (@telefoot_TF1) October 18, 2020
Kylian Mbappé à propos des retrouvailles avec Cavani en Ligue des Champions pic.twitter.com/fYS8avI6Kl
Speaking to Telefoot ahead of the potential showdown with Cavani, Mbappe was short on sentiment.
"He's on another team now. I wish him the best, but he's not one of us anymore. We're going to play against him, and we'll try to beat them."