Cahill, 32, who last month departed Everton after eight seasons to play for New York Red Bulls, had indicated he did not want to be considered for Socceroos friendlies until he settled into his new life.
Kewell's omission was more expected after cutting ties to Melbourne Victory and moving back to England, where he is hoping a club will sign him.
Coach Holger Osieck indicated both players still had a future with Australia.
"It's very unfortunate for him that he's waiting with no club, and still waiting for a signing," he said of Kewell, 33. "Still, I think he has great potential and whenever I have him in the group, he's a very positive asset."
The coach said Cahill's move could prove a boon for the Socceroos.
"He opted for a new challenge, he thinks it's a good move for him," he said. "Major League Soccer is becoming stronger and stronger. He's going to be forced to show his best and that will be positive for the Socceroos as well."
While Kewell and Cahill will be missing, captain Lucas Neill, who is also without a club, was selected, along with veteran goalkeeper Mark Schwarzer, who should win his 99th cap in the friendly on 15 August.
Osieck also included some new faces, including Jason Davidson, a 21-year-old defender who has spent three years in Portugal and the Netherlands, breaking into the Heracles Almelo first team last season, and uncapped Aston Villa defender Chris Herd.
Fellow defender Ryan McGowan, who plays for Scottish club Hearts, was also picked for the first time.
Goalkeepers: Adam Federici (Reading/England), Mitchell Langerak (Borussia Dortmund/Germany), Mark Schwarzer (Fulham/England)
Defenders: David Carney (Bunyodkor/Uzbekistan), Jason Davidson (Heracles Almelo/Netherlands), Chris Herd (Aston Villa/England), Lucas Neill (unattached), Ryan McGowan (Hearts/Scotland), Sasa Ognenovski (Umm Salal/Qatar) Luke Wilkshire (Dinamo Moscow/Russia), Rhys Williams (Middlesbrough/England)
Midfielders: Mark Bresciano (Al Gharafa/Qatar), Brett Holman (Aston Villa/England), Mile Jedinak (Crystal Palace/England), Neil Kilkenny (Bristol City/England), Carl Valeri (Sassuolo/Italy)
Forwards: Alex Brosque (Shimizu S-Pulse/Japan), Robbie Kruse (Fortuna Dusseldorf/Germany), Scott McDonald (Middlesbrough/England), Archie Thompson (Melbourne Victory)