Real Madrid defender Raphael Varane is expected to be sidelined for three weeks after suffering a hamstring injury against Shakhtar Donetsk in the Champions League.
Varane, 22, came off in the 33rd minute of the Spanish giants' 4-3 victory in Ukraine on 25 November.
Spanish daily Marca reported that the France international could miss up to six of Real's matches across La Liga, the Copa del Rey and the Champions League.
The news is a major blow for coach Rafael Benitez, who is already without defenders Marcelo and Sergio Ramos due to injury.
"After tests carried out today on the player Raphael Varane... he has been diagnosed with a muscle injury in his right thigh. His recovery will continue to be assessed," a statement on Real's official website said.
Benitez is likely to deploy Pepe and Nacho in central defence for the Eibar match on 29 November, with Dani Carvajal and Danilo likely to start in the full-back positions.
Madrid's defensive lapses of late are a cause for concern for Benitez, who has seen his side concede 10 goals in the last three matches - including three in the final 13 minutes against Shakhtar.
The former Liverpool boss put the late concessions down to complacency, saying "anyone might have felt that the game was won" with the score line at 4-0.
"Reacting the way the team did after the game against Barcelona and going 4-0 up in the Champions League is really positive. Their goals are two lapses in concentration that could have been avoided, that's all there is to it," he was quoted as saying by Real's website after the match.
"We were on top in every department until we made the mistake that led to the penalty, and then they quickly scored a second and grew in confidence.
"I don't want to forget that we are group winners and have won away in the Champions League with four goals scored. I leave here with a very positive feeling."