Real Madrid winger Vinicius Junior suffered ruptured ligaments in Tuesday's Champions League defeat to Ajax and could be out until May.
The Brazilian forward limped off in tears in the 35th minute of the 4-1 home loss to Ajax and was replaced by Marco Asensio.
The 18-year-old, who was injured in a challenge with Noussair Mazraoui, underwent tests on Wednesday, and a statement from Real Madrid read: "After tests done today to our player Vinicius Jr by Real Madrid's medical team, he has been diagnosed with ruptured ligaments in his tibiofibular joint of his right leg."
Madrid have not confirmed the length of Vinicius' absence but it is expected he will be out for around two months, so is expected to miss Brazil's upcoming friendlies against Panama and Czech Republic, his first call-up to the senior squad.
Lucas Vazquez, who left the pitch in the 29th minute of Tuesday's game with a suspected hamstring injury, and Gareth Bale are also expected to undergo tests on Wednesday. Bale sustained a right ankle problem and could not finish the match. Dani Carvajal has also joined the walking wounded after a bruising week, after tests confirmed he has a hamstring tear as well.
All are expected to sit out Sunday's league game at Real Valladolid with Madrid third in La Liga, 12 points adrift of league leaders Barcelona after 26 rounds.