PSG said on Thursday Mbappe would be out for three weeks after sustaining a thigh injury. He had limped off during the first half of PSG's 3-1 win at Montpellier on Wednesday.
"I don't think he will be missing (against Bayern) so I expect nothing else," Nagelsmann told a news conference. "I don't know what he has so I assume he will play. It is a bit vague on their (PSG's) homepage saying he would be out for up to three weeks."
Mbappe is joint top scorer in the Champions League with seven goals, and second in Ligue 1 with 13 in nine matches played.
"If there is no structural injury I can't see him missing the game," Nagelsmann said. "It is too early to say already now that he won't play if there is no structural injury."
He said the fact that there was no specific injury named could be part of a plan by the French club.
Bayern, top of the Bundesliga with a one-point lead, will host PSG on March 8th in the return leg.
PSG are due to play five matches from February 4th-19th, with the France international also set to miss their French Cup last-16 game against Olympique de Marseille.