Mbappe sustained a hamstring injury in Thursday's (AEDT) Ligue 1 clash with Montpellier. PSG subsequently announced the 24-year-old is set to be sidelined for around three weeks.
If that estimated recovery time is accurate, Mbappe would be unavailable for the first leg of PSG's clash with Bundesliga champion Bayern on 15 February (AEDT).
However, Bayern coach Nagelsmann is not fully convinced that will be the case.
"I don't think he will be out, I don't expect anything else. I don't know what [injury] he's got, I assume [he will be] playing," Nagelsmann said ahead of Bayern's trip to Wolfsburg on Sunday (AEDT).
"I don't know what he has. It's relatively vague on the PSG website. If it's not a structural injury, I can't imagine him missing the game, but I don't know. Of course, they can play poker.
"I am preparing for the game as if he is going to play."
While Nagelsmann does not fully believe PSG's news about Mbappe, he could be seen as playing mind games of his own, as he revealed Sadio Mane will not be fit to feature against the French champion.
Mane missed the FIFA World Cup because of an injury sustained while in action for Bayern just ahead of the tournament but returned to training last month.
"I am expecting him back in the middle or at the end of February," Nagelsmann said of the former Liverpool attacker.
"Things are looking good and he's pain-free. He will definitely miss the first leg against PSG."
Bayern claimed its first win of 2023 in emphatic fashion last time out, beating Mainz 4-0 in the DFB Pokal.
It has drawn its three Bundesliga matches since the season's resumption, but faces a Wolfsburg team that has lost its past two games.
Making his debut after a loan move from Manchester City, Joao Cancelo impressed against Mainz, and Nagelsmann had praise for his latest recruit.
"He's a very likeable player and will help better us," he said.
"He's a fighter who likes to play as much as possible and who wants to impact the game. He adds new options to our team. He was very strong in the first half against Mainz."
