The club have announced that their manager suffered a sprained ankle and a broken bone in his foot during PSG's training session on Thursday night.
"Thomas Tuchel was the victim last night of a sprained left ankle with a fracture of the fifth metatarsal during a sporting session," PSG said in a statement on Twitter.
Tuchel will still be present on Wednesday when PSG face Atalanta in a quarter-final showdown in Lisbon, but several of his side's top performers are in doubt for the game.
Mbappe was facing a three-week absence after the injury, which would not give him sufficient time to recover for the match against Atalanta.
Earlier this week, Tuchel said he was unclear on Mbappe's status but that he did "not expect too much" in terms of the 21-year-old being ready for the game.
Mbappe, though, is not the only injury doubt for the match after Marco Verratti suffered an injury in training on Tuesday.
"[Verratti was] the victim of a severe shock yesterday in training," the club announced, "with a significant right calf contusion resulting in muscle damage which will be assessed in the next 72 hours."
In addition, left-back Layvin Kurzawa is out for the game with a thigh muscle injury, while Thilo Kehrer will also miss out after suffering a bone fracture near his ear.