Real Madrid forward Jese Rodriguez suffered cruciate ligament damage to his right knee in his side's 3-1 win over Schalke, Real coach Carlo Ancelotti confirmed on Tuesday.
The Spanish under-21 international collapsed under a challenge from Sead Kolasinac after just two minutes.
He was then carried from the field on a stretcher after briefly trying to put weight on the injured knee.
"I think it is confirmed he has ruptured cruciate ligament," said Ancelotti.
"He has had bad luck and it is bad luck for Real Madrid because we are going to lose a very important, young player who has done very well this season and surprised everyone."
Jese had become an important member of Ancelotti's squad in his first season with the senior team, scoring eight times in all competitions.
However, he is now expected to be out of action for six months ending his outside chances of being included in Vicente del Bosque's squad for the World Cup in Brazil later this year.