According to a statement on the Brazilian football federation website, Marcelo is likely to be out of action for around three months after damaging his foot during training with the national team in Poland on Sunday.
Marcelo has now returned to Madrid where he will undergo further tests with the Spanish champions.
A Madrid statement read: "The left-back has suffered a fracture in his right foot, the Brazilian football federation (CBF) have announced in a statement.
"Marcelo suffered the injury while taking part in a training session with the Brazil national team in the Polish city of Wroclaw on Sunday.
"The Brazilian underwent tests at a local hospital which revealed he had fractured the fifth metatarsal of his right foot.
"The player, who immediately returned to Madrid, will be placed in the hands of the club's medical staff, who will verify the extent of the injury and determine what course of treatment the player will follow."