Jockey Michelle Payne has been ruled out of the Shergar Cup team event at Ascot on 6 August after a serious fall.
Payne, who became the first female rider to win the Melbourne Cup in November, is recovering in hospital after abdomen surgery.
The 30-year-old had already been ruled out of a Royal Ascot debut in May.
Des O'Keeffe, general manager of the Australian Jockeys' Association, said Payne "had her heart set" on riding at Royal Ascot and in the Shergar Cup.
He told BBC Sport: "There's always 2017 and hopefully she'll be lucky enough to be invited again then."
Payne is described as being in a "serious but stable" condition in hospital after suffering internal injuries when she was dislodged from her horse Dutch Courage at Mildura Racceourse.
Payne was scheduled to be part of a team of female jockeys looking to retain the Shergar Cup, competing against male riders representing Great Britain and Ireland, Europe and the Rest of the World.