The French forward suffered the injury in Friday’s French Cup final win over Saint-Etienne following a challenge by Loic Perrin, leaving the 21-year-old in tears as he left the pitch.
A statement from the French club read: ”Serious right ankle sprain to the external lateral compartment. To be re-evaluated in 72 hours with clinical and ankle imaging analysis.”
The news a crushing blow for Thomas Tuchel, who is preparing his side to face Atalanta on 12 August in the quarter-final of the Champions League in Lisbon.
While Mbappe also looks set to miss the French League Cup final against Lyon on 31 July.
Mbappe was heard telling French President Emmanuel Macron, “It went crack”. Macron then asked whether anything was broken and Mbappe responded ”No, I don’t think so.”
Tuchel labelled the rough treatment handed out by Saint-Etienne players as “horrible”.
“It was complicated with all the fouls to Thilo Kehrer, Neymar and Mbappe,” Tuchel said.
“In the last three matches against St Etienne 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.
“We won and we have a lot of things to improve, to talk about and analyse.”
Mbappe took to social media to celebrate adding another piece of silverware, rather than dwell on his injury.
He said: “Awakening as a winner, no better feeling possible. Thank you all for your messages, it touches me a lot. Kisses to all and have a good weekend.”