Los Blancos and Les Bleus agreed for Mbappe to return to the Spanish capital for immediate treatment, but his period of absence remains unconfirmed.
"After tests carried out today by Real Madrid's medical department on our player Kylian Mbappe, he's been diagnosed with a hyperextension of the posterior capsule of his left knee," an statement confirmed.
However, despite initial assessments indicating Mbappe would be able to train ahead of the October 10th clash with Villarreal, that is now in serous doubt.
As per Mundo Deportivo, Mbappe has been back in Madrid for five days and not trained, but he was spotted at party last Wednesday in Paris with his partner, Ester Expósito.
There is no rumoured concern over that, with Jose Mourinho sanctioning a break, as his non-international players all training in Valdebebas.