Published: 2020-07-28 03:18:34 BdST
It means Mbappe will miss PSG's Champions League quarter-final against Italian side Atalanta in Lisbon on Aug. 12.
"The results of today's scan confirmed an ankle sprain with damage to the external ligament. The player is expected to be sidelined for approximately three weeks," PSG said in a statement.
A rough tackle from Loic Perrin saw the St Etienne defender catch Mbappe on the ankle and the 21-year-old collapsed on the pitch in pain before being substituted.