Michelle Payne will not compete in the Shergar Cup team jockeys challenge at Ascot because of illness.
She was scheduled to ride in the Shergar Cup a year ago but had not recovered from serious injuries suffered in a race fall a few months earlier.
"They wouldn't let me leave, " Payne told NewsCorp.
"I would like to thank everyone for their support and encouragement and would love to return another time".
Payne, who created history when becoming the first woman to ride the victor of the Melbourne Cup, on Prince Of Penzance in 2015, left a press conference early on Thursday as she was feeling unwell, saying that she had picked up a bug.
Ascot Head of Communications Nick Smith said, "Michelle is feeling a little better today, I understand, and hopefully by tomorrow she'll be fighting fit".
Ascot head of communications Nick Smith said he hoped she would be well enough to ride in the worldwide jockeys team challenge on Saturday (Sunday AEST).
Payne will ride Melbourne-bound Kaspersky at the Newbury meeting.
Payne's brother-in-law Kerrin McEvoy is the captain of the Rest of the World team.