Real Madrid confirmed that defender Eder Militao will undergo surgery after sustaining an anterior cruciate ligament (ACL) tear in their 4-0 win over Osasuna.
Militao was forced off in the 30th minute of their LaLiga clash at the Bernabeu on Saturday after hyperextending his knee in an attempt to reach the ball.
The Brazilian, who missed six months of last season with a serious knee injury, received treatment on the pitch before being stretched off with tears in his eyes.
He becomes the second Madrid player to suffer an ACL injury this term after Dani Carvajal was sidelined for the rest of the campaign last month.
"Following tests carried out today on our player Eder Militao by the Real Madrid Medical Services, he has been diagnosed with a complete rupture of the anterior cruciate ligament with involvement of both menisci in his right leg. Militao will undergo surgery in the coming days," Real Madrid said in a statement.
Either side of Militao's injury, team-mates Rodrygo and Lucas Vazquez were also forced off the pitch, overshadowing a much-needed return to winning ways.
Carlo Ancelotti said he will be looking to bring in some of the club's youth academy players into the first-team picture to fill the gaps in their injury-hit squad.
Madrid are also without Thibaut Courtois, Aurelien Tchouameni and David Alaba through injury, though Ancelotti was not thinking about making new signings in January.
"I'm not thinking about signings right now because we have to prepare for games with the players we have," Ancelotti told a press conference.
"Three injuries in the first half is quite rare. The demanding schedule doesn't allow the players to rest and be fresh.
"We will evaluate the situation in the coming months. The only thing we can do is try to recover as many players as possible. We will see in January what happens."
"Today (academy defender) Raul Asencio came off the bench and made a good contribution, (midfielder) Federico Valverde played fine as a full back.
"We did well last year when we had injuries, and we will do the same this year as well."