“Following tests carried out on our player David Alaba, he has been diagnosed with a torn anterior cruciate ligament in his left knee,” Real said late on Sunday.
“He will undergo surgery in the coming days.”
This could mean the end of the season for the Austrian defender, while it is also doubtful that he will be able to take part in the European Championships in Germany from June 14 to July 14.
Alaba was injured in the first half of the 4-1 home win against Villarreal on Sunday and had to be substituted.
Madrid manager Carlo Ancelotti spoke afterwards of “very sad news”.
Alaba’s teammate Toni Kroos wrote on the social media platform X, formerly Twitter: “I love you, @David_Alaba.”
Real have taken a one-point lead over Girona at the top of the table, although the Catalan team can reclaim the lead in Monday’s match against Alaves.
