Simon had been recalled for the friendlies against South Africa and Denmark, in London and Viborg on Saturday and Tuesday respectively. But the Tottenham forward was substituted after a nasty collision during Sunday's 2-1 win over Reading.
She was one of four Matildas ruled out of the games on Monday. Football Australia is awaiting further information from the club about the extent of Simon's injury. Emily van Egmond (quad strain), Tameka Yallop (ankle) and Clare Wheeler (knee) have also been withdrawn from the squad due to injuries sustained at club level.
Forward Remy Siemsen and defenders Emma Checker and Matilda McNamara will replace them in a squad seeking a return to form after back-to-back losses in Australia to Canada last month.
Stockholm-based Siemsen, 22, has earned six caps, Checker (eight caps) has not played for the Matildas this year and Denmark-based McNamara will be looking to earn her debut ahead of next year's home World Cup.