Purton was kicked by a horse last Wednesday at the trials in Hong Kong and scans have revealed the top rider has a fracture and torn ligaments in his right ankle.
Purton was due to return for next Saturday's Group I meeting where he was booked to ride the Gary Portelli-trained Sebring Sun in the $1 million contest.
Purton has also secured the mount on the Peter and Paul Snowden-trained Bounding in the Sheraco Stakes and two rides for leading trainer Chris Waller -
"If it was up to me, I'd be back riding at the trials on Saturday, let alone Sunday - I feel that good," Purton told the South China Morning Post.
"But the scan says otherwise, so I have to listen to the advice of the doctors and rest it.
"It's really disappointing. I had good rides on Sunday and the following week as well and I was hoping to start (the Hong Kong season) with a bang.”
Sebring Sun's trainer Gary Portelli said he hasn't finalised a replacement for Purton.