Real Madrid have announced David Alaba has suffered an anterior cruciate ligament injury.
Alaba broke down in yesterday's win against Villarreal.
And Real Madrid announced on Monday: "After tests, our player David Alaba has been diagnosed with a rupture of the anterior cruciate ligament of the left knee.
"The player will undergo surgery in the coming days."
For the moment, Real have two fit centre-halves - Nacho Fernandez and Toni Rudiger.
