Marcelo was forced off in Real Madrid's 1-1 draw with Villarreal, and tests have confirmed he has sustained a grade two calf muscle strain.
Real Madrid have confirmed that full-back Marcelo has suffered a calf muscle strain.
The Brazil international, who had played every minute of Madrid's opening six games this season, was forced off in the first half of Wednesday's 1-1 draw with Villarreal after pulling up in discomfort.
"Following tests carried out today on Marcelo at the Sanitas La Moraleja University Hospital, he has been diagnosed with a grade two muscle strain in the soleus muscle of his right calf," a Madrid statement read. "His recovery will continue to be monitored."
Initial reports in Spain have suggested that Marcelo will be sidelined for between two and three weeks.
He will miss Saturday's trip to Las Palmas and is expected to be unavailable for the Champions League clash with Borussia Dortmund next week, or the league match at home to Eibar on October 2.
The news comes as a blow for head coach Zinedine Zidane, with midfielder Casemiro having been diagnosed with a leg fracture this week, while centre-back Pepe is still short of full fitness.