Real Madrid's Dani Carvajal will undergo surgery after rupturing two ligaments and a tendon in his right leg, the LaLiga club has said.
The defender was substituted during Saturday's 2-0 win over Villarreal.
Carvajal, 32, was stretchered off in stoppage time after he twisted his right knee during a duel with Villarreal midfielder Yeremy Pino.
"Serious cruciate ligament injury confirmed, I'll have to undergo surgery and be off the field for a few months," Carvajal said on Instagram, where he also posted a picture of himself in an ambulance.
"Looking forward to starting the recovery process and coming back like an animal. Thank you all for your messages, I feel very loved," he added.
Coach Carlo Ancelotti said he was concerned about Carvajal's injury, the latest blow for the Spanish side after they played without goalkeeper Thibaut Courtois, who suffered an abductor muscle injury against Atletico last weekend.
In a statement on Sunday, Real said Carvajal had been "diagnosed with a ruptured anterior cruciate ligament, a ruptured external collateral ligament and a ruptured popliteal tendon in his right leg."
The LaLiga club also said that winger Vinicius Jr. had suffered a cervical injury in the same match.
Real are second in the standings, level on 21 points with leaders Barcelona, who visit 11th-placed Alaves later on Sunday.