Osieck left out Kewell in a 23-man squad for the opening match against Thailand in Brisbane on 2 September, followed by a game with Saudi Arabia in Dammam four days later.
Osieck said Kewell, 32, would return to the national squad as soon as he regained match fitness with his new Australian A-League club Melbourne Victory.
"He definitely is healthy but, to be physically healthy and match fit, it's always a gap," Osieck said. "I cannot give you an update on his match fitness. I simply know Victory will expect him in early September to join team training."
Kewell linked up with Victory in a three-year deal last weekend after a 15-year playing career in Europe with Leeds, Liverpool and Galatasaray in Turkey.
First-choice stars Brett Holman, Josh Kennedy and Sasa Ognenovski were named to make their return in Australia's opening two qualifiers for the 2014 FIFA World Cup. Holman, Kennedy and Ognenovski were recalled after missing the 2-1 friendly win over Wales earlier this month through injuries and club commitments.
The squad features senior trio Tim Cahill, skipper Lucas Neill and Mark Schwarzer as well as youth in Adam Sarota and Luke DeVere, with Osieck saying he had picked his strongest available squad for qualification for the 2014 finals in Brazil.
"From my point of view, it's the strongest group we have at the moment," Osieck said. "We need to be strong, we are starting our new World Cup campaign... I think it's already a pretty difficult start."
The squad includes the entire playing group that featured against Wales in Cardiff, with defender Mark Milligan and goalkeeper Nathan Coe also added.
Australia's opening qualification group also includes Oman with the top two teams to progress to the final round of Asian qualification.
Goalkeepers: Nathan Coe (Sonderjysk/Denmark), Adam Federici (Reading/England), Mark Schwarzer (Fulham/England)
Defenders: Luke DeVere (Gyeongnam/Korea Republic), Matt McKay (Brisbane Roar), Mark Milligan (JEF United/Japan), Lucas Neill (Al-Jazira/UAE), Sasa Ognenovski (Seongnam Ilhwa Chunma/Korea Republic), Matthew Spiranovic (Urawa Red Diamonds/Japan), Luke Wilkshire (Dinamo Moscow/Russia), Rhys Williams (Middlesbrough/England), Michael Zullo (Utrecht/Netherlands)
Midfielders: Brett Emerton (Blackburn Rovers/England), Brett Holman (AZ Alkmaar/Netherlands), Mile Jedinak (Crystal Palace/England), Neil Kilkenny (Bristol City/England), Adam Sarota (Utrecht/Netherlands), James Troisi (Kayserispor/Turkey), Carl Valeri (Sassuolo/Italy)
Forwards: Tim Cahill (Everton/England), Josh Kennedy (Nagoya Grampus/Japan), Robbie Kruse (Fortuna Dusseldorf/Germany), Scott McDonald (Middlesbrough/England)