Published : 23 Sep 2016, 08:02 PM
The Brazil international was substituted in Real's 2-0 win over Espanyol on Sunday and played no part in Wednesday's 1-1 draw with Villarreal.
"Following tests carried out today on Casemiro at the Sanitas La Moraleja University Hospital, he has been diagnosed with a fracture to the central third of his left fibula. His recovery will continue to be assessed," the club said in statement.
The 24-year-old, who has made five appearances in all competitions for Madrid this season, is likely to miss Brazil's World Cup qualifiers against Bolivia and Venezuela next month.