Brazil right-back Danilo has been ruled out for the remainder of the World Cup after suffering ligament damage in his left ankle during training on Thursday.
The Manchester City man injured the ankle during a training activity and was taken aside for medical evaluation by team doctor Rodrigo Lasmar.
The Brazilian Football Confederation later said the exams showed ligament damage and that Danilo would not recover in time to play another game at the tournament.
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Danilo, who started Brazil's tournament opener against Switzerland, had missed the past three matches with a thigh problem and had recently returned to full training with the squad.
The injury leaves Fagner, who filled in while the former Real Madrid defender was out, the only natural right-back on the team, although Marquinhos can slide over if needed.
Danilo's is the second World Cup-ending injury at the position for manager Tite's side. Regular starter Dani Alves was ruled out with a serious knee injury a month before the tournament began.
On the other side of the defence, left-back Marcelo has only just worked his way back after exiting last week's match against Serbia with back spasms and missing the Selecao's 2-0 round-of-16 defeat of Mexico.
Tite confirmed on Thursday the Real Madrid defender will return to the starting XI for Brazil's quarterfinal clash against Belgium on Friday, while Fernandinho will take the place of the suspended Casemiro in midfield.
The former Corinthians coach added that the versatile Marquinhos is also capable of playing as a defensive midfielder if needed.
"Marquinhos can play also as the first midfielder, and I think in his first game with me at Corinthians he played there. He knows what to do," Tite said.
Forward Douglas Costa will also be available for the quarterfinal after recovering from a right thigh muscle injury that prevented him from playing against Serbia and Mexico.
Brazil will enter the match with the lineup of Alisson at goalkeeper; Fagner, Thiago Silva, Miranda and Marcelo in defence; Fernandinho, Philippe Coutinho and Paulinho in midfield; and Willian, Neymar and Gabriel Jesus in attack.
Information from the Associated Press was used in this report.