Brazil defender Danilo has been ruled out of Friday's Group E game with Costa Rica with a thigh problem and will be replaced by Corinthians right back Fagner, the Brazilian Football Confederation said on Thursday.
Danilo, who was promoted to a starting role after Dani Alves pulled out of the squad with an injury in May, tweaked his right thigh during training, team doctor Rodrigo Lasmar said.
He will undergo physiotherapy treatment immediately but a firm date for his return was not given.
Brazil face Costa Rica in St Petersburg needing a win after a disappointing 1-1 draw with Switzerland in their opening game. The Costa Ricans lost their first group match 1-0 to Serbia.
Brazil named Paris St Germain defender Thiago Silva as captain for the match in a continuation of their long-standing policy of rotating the team leadership.
He last wore the armband during a 1-0 defeat by Argentina in June, that friendly loss in Australia being the only defeat suffered by coach Tite's Brazil in the last 22 games.