Marcelo could miss up to a month with a hamstring injury that Real Madrid confirmed on Wednesday.
The left-back suffered the injury over the weekend in Madrid's 5-1 defeat at the hands of Barcelona.
As a result, the Brazilian has been left out of the team's squad for Wednesday's Copa del Rey match against Melilla.
While the club has yet to announce an official timetable, the defender is expected to miss roughly 3-4 weeks
"Following tests carried out on Marcelo by the Real Madrid Medical Services, he has been diagnosed with a muscular injury to his right hamstring," the club said in a statement.
"His recovery will continue to be assessed."
The club is currently dealing with a number of injury issues, including Raphael Varane, who could miss up to a month with an adductor injury.
Mariano Diaz is also out for Real Madrid as the striker picked up an injury to his right bicep.
The club has been hit by a number of muscle injuries this campaign with Jesus Vallejo, Gareth Bale, and Dani Carvajal all spending time in the treatment room for similar problems.
Wednesday's Copa del Rey match is the first under Santiago Solari, who replaced the sacked Julen Lopetegui following the Clasico loss.