Oscar has been left out of Brazil's squad for the 2015 Copa America after manager Dunga confirmed the Chelsea midfielder suffered an injury during a recent training session with his club.
The 23-year-old, who has already earned 45 senior international caps in his career to date, was involved in a heavy collision with Arsenal goalkeeper David Ospina during the Premier League champions' goalless draw at the Emirates Stadium on 26 April but was listed among the substitutes at Leicester City three days later.
He was not named in the matchday squad for Chelsea's title-clinching 1-0 victory over Crystal Palace at Stamford Bridge, though, and it is unclear at this stage how long he will take to recover from this latest setback.
"He had an injury in his last training session with Chelsea," Dunga, now in his second spell in charge of his native Brazil following their humiliation in the semi-finals of the 2014 World Cup, claimed on the competition's official website.
"We talked to Mourinho and with the Chelsea doctors. His period of recovery will be somewhat prolonged, so he will not be in the best condition. We think he will be better prepared for the World Cup qualifiers, which begin soon after the Copa América."
Oscar took to Instagram after the announcement, expressing sorrow that he will not be able to help his country in their quest to win back a trophy they last held in 2007 following victory over fierce rivals Argentina.
"I am very sad that I can not defend my country in the Copa America, because of this injury," he said. "I'll be cheering for my teammates can bring this title for us. Thank you all for caring and for incoming messages, then I'll be back."
With Oscar unavailable for the first summer in four years, Brazil have kept faith with Liverpool playmaker Philippe Coutinho for the upcoming tournament.
There is no place for Ramires in the 23, meanwhile, but Chelsea teammate Willian is included alongside Manchester City's Fernandinho, Everton Ribiero from Al-Ahli and Casemiro of Porto.
Santos striker Robinho retains his place after earning a recall in March, while uncapped Arsenal centre-back Gabriel is not selected after previously providing squad cover for Paris Saint-Germain duo David Luiz and Marquinhos for recent friendly matches against France and Chile.
The latest edition of the Copa America takes place in Chile and is scheduled to start on 11 June.
Brazil have been placed in Group C alongside Colombia, Peru and Venezuela while holders Uruguay are in Group B with Paraguay, guest nation Jamaica and Argentina.
Brazil squad for 2015 Copa America
Goalkeepers: Jefferson (Botafogo), Diego Alves (Valencia), Marcelo Grohe (Grêmio)
Defenders: Fabinho (Monaco), Marcelo (Real Madrid), Filipe Luis (Chelsea), Danilo (Porto), David Luiz (PSG), Marquinhos (PSG), Thiago Silva (PSG), Miranda (Atletico de Madrid)
Midfielders: Luiz Gustavo (Wolfsburg), Elias (Corinthians), Fernandinho (Manchester City), Casemiro (Porto), Willian (Chelsea), Philippe Coutinho (Liverpool), Everton Ribeiro (Al-Ahli), Douglas Costa (Shakhtar Donetsk)
Forwards: Neymar (Barcelona), Robinho (Santos), Roberto Firmino (Hoffenheim), Diego Tardelli (Shandong Luneng)