Cooney-Cross was one of the biggest names left off the 26-player roster to face world No.3 Germany and world No.47 Haiti in Europe next month, along with injured duo Alanna Kennedy and Charlize Rule.
The omission follows her return to Arsenal this month after taking a break to be with her mother, who died from cancer in July.
The midfielder hasn't played in the national team since the AFC Women's Asian Cup final in March.
"She was thinking about coming in October. We discussed it, and we just felt it was a little bit too early," Montemurro said on Thursday.
"She's in a really good space at the moment, and she'll be back.
"We've really left it to her and how she feels."
Montemurro named three uncapped players, including midfielder Hana Lowry, who suffered a gut-wrenching ACL injury on the eve of her potential Matildas debut in 2024.
The 23-year-old inked a deal to move from A-League Women club Sydney FC to Norway this year and has impressed, scoring a goal and assisting another in her first seven games.
"Going to Vålerenga was a really important step for her, and I went to visit a couple of weeks ago," Montemurro said.
"(She's) really grown, really stabilised as a player that's comfortable with the ball, but also someone that I believe has a great attitude and character, to really be a top-level footballer."
Melbourne Victory's Courtney Newbon is another potential debutant as goalkeeper Teagan Micah continues to build from a stint on the sidelines, while defender Tori Tumeth also received a maiden call-up.
Midfielder Isabel Gomez and goalkeeper Ilona Melegh have been dropped after they were part of the side for the two-game series against Mexico in June.
Defenders Charli Grant and Alexia Apostolakis, along with midfielder Daniela Galic, return to the national set-up.
European stars Mary Fowler, Caitlin Foord, Ellie Carpenter and Steph Catley have also been named, as has Gotham City's Sam Kerr.
The October international window shapes as a crucial point in the Matildas' preparation for the FIFA Women's World Cup, which starts in Brazil in June.
There are only a handful of international breaks before the showpiece tournament, meaning every game is crucial for Australia as they look to build on their fourth-place finish in 2023.
MATILDAS SQUAD: Alexia Apostolakis, Mackenzie Arnold (GK), Ellie Carpenter, Steph Catley, Alex Chidiac, Caitlin Foord, Mary Fowler, Daniela Galic, Charli Grant, Winonah Heatley, Sam Kerr, Chloe Lincoln (GK), Hana Lowry, Leticia McKenna, Holly McNamara, Alana Murphy, Courtney Nevin, Courtney Newbon (GK), Jamilla Rankin, Hayley Raso, Amy Sayer, Remy Siemsen, Kaitlyn Torpey, Tori Tumeth, Emily van Egmond, Clare Wheeler.
