Paris Saint-Germain defender David Luiz is in a race against time to be fit for Brazil's 2018 World Cup qualifier against Venezuela on Tuesday.
Luiz left the pitch in the 35th minute of the Selecao's 2-0 loss to Chile in Santiago on Thursday in the opening match of their qualifying campaign, Xinhua news agency reported.
His replacement, PSG teammate Marquinhos, said he was unsure if Luiz would be ready in time to take on the Vinotinto in Fortaleza.
"I have not had any other news other than the problem was diagnosed," Marquinhos said.
"He has some pain in the knee. We will only really know exactly how he is over the coming days."
Venezuela began their quest for a World Cup berth in Russia with a 1-0 home loss to Paraguay.
Brazil will still be without captain Neymar for Tuesday's fixture as he serves the last match of a four-game ban.
