Barcelona striker Neymar is suspended for both matches and was left out, although an appeal is pending.
"We would like to have Neymar but that's not possible," Dunga told reporters. "We need to get behind the players we have."
Dunga has subjected his 23-man squad to yet more chopping and changing.
Chelsea midfielder Ramires was left out after appearing in the squad that beat Costa Rica 1-0 and the United States 4-1 earlier this month, and Atletico Madrid's Filipe Luis was recalled after missing that double-header.
Kaka, who missed the Copa America in June and July, was surprisingly recalled for the Costa Rica and U.S. games but the Orlando City midfielder has been left out again.
"We used 55 players in the last qualifiers, so some that are not in this first call up, there will be a long preparation period, and they should be ready, they will have a chance," Dunga said.
Renato Augusto, one of the stars of Corinthians' rise to the top of Brazil's Serie A, is included for the first time since 2011, and centre half Gil returns after missing the Copa America.
The South American qualifiers are in a round-robin format with all 10 teams facing each other home and away.
Brazil, who have never failed to qualify for the finals, kick off their campaign away to Copa America champions Chile on Oct. 8 and then face Venezuela in Fortaleza five days later.
Squad:
Goalkeepers: Jefferson (Botafogo), Marcelo Grohe (Gremio), Allison (Internacional)
Defenders: David Luiz (Paris St Germain), Marquinhos (Paris St Germain), Miranda (Inter Milan), Gil (Corinthians), Filipe Luis (Atletico Madrid), Fabinho (Monaco), Rafinha (Bayern Munich), Marcelo (Real Madrid)
Midfielders: Luiz Gustavo (VfL Wolfsburg), Fernandinho (Manchester City), Elias (Corinthians), Renato Augusto (Corinthians), Oscar (Chelsea), Willian (Chelsea), Lucas Lima (Santos) Philippe Coutinho (Liverpool), Douglas Costa (Bayern Munich)
Forwards: Lucas (Paris St Germain), Hulk (Zenit St Petersburg), Firmino (Liverpool)
(Writing by Andrew Downie; editing by Toby Davis)
