Michael Kinane will miss the ride on Giant's Causeway in tomorrow's Coral-Eclipse Stakes but is confident he will be fit for the start of the July meeting at Newmarket next Tuesday.
George Duffield has been booked to take the Irishman's place on board the St James's Palace Stakes winner in the Sandown Group One event.
Kinane has been sidelined since tweaking a muscle in his back at the Curragh last Saturday.
John Hanmer, who books Kinane's rides in Britain, explained it was a "cautious decision" on the jockey's part.
"He was 95 per cent fit this morning but he doesn't want to ride if he is not 100%," Hanmer said.
"If he's not 100 per cent it could set him back but he's very confident that he'll ride at Newmarket on Tuesday, maybe before.
"It was a cautious decision, he could probably get away with it but he didn't want to risk it."
Duffield also substituted for Kinane on Irish Derby second Ciro at the Curragh, and won the Racing Post Trophy for O'Brien on Aristotle last October.
The news did not come as a shock to the jockey.
He said: "I was offered the ride a day or two back if Michael didn't pass the doctor so it didn't come as a complete surprise. I'm very pleased.
"He's a class horse _ ordinary horses don't win the St James's Palace Stakes.
"Sakhee has to take the beating with the Derby form being franked and he'll stay the trip and a bit further.
"But I'd think Giant's Causeway would have a good chance."
Duffield has tasted success in the race before, partnering Environment Friend to victory for trainer James Fanshawe in 1991.
