Paris Saint-Germain suffers Kylian Mbappe injury blow ahead of Champions League
The 21-year-old limped out of Friday's French Cup final win against Saint-Étienne following a late tackle from Loic Perrin, who was shown a red card for the challenge.
"The results of today's scan confirmed an ankle sprain with damage to the external ligament," said PSG in a statement. "The player is expected to be sidelined for approximately three weeks."
PSG's Champions League campaign resumes on August 12 against Atalanta, with all matches in the competition's altered format now being played over one leg instead of two.
"It was complicated with all the fouls to Thilo Kehrer, Neymar and Mbappé," Tuchel told reporters after the match following PSG's 13th French Cup title, which came courtesy of Neymar's 14th-minute winner.
Mbappe was on crutches and wearing a protective boot during the trophy ceremony
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"In the last three matches against Saint-Étienne they get a red card in the first 30 minutes. I don't know what is being said in their dressing room. It is horrible, I can't understand it," added Tuchel.
PSG is chasing an unprecedented quadruple of trophies. With the Ligue 1 title and French Cup already wrapped up, PSG will face Lyon on Friday in what will be the last ever League Cup final.
Mbappe, who signed from Monaco for a reported $214 million in 2017, has scored 29 goals for PSG this season and, alongside Neymar and Mauro Icardi, forms part of one of the most prolific attacking lines in Europe.