“Frankie is not certain to sit around and see if the rain comes or not and therefore has asked his agent to book him for rides at Doncaster,” said Harry Herbert, racing manager to Motivator’s owners, the Royal Ascot Racing Club.

Dettori came in for the ride aboard Michael Bell’s charge after regular partner Johnny Murtagh was ruled out when picking up a 21-day suspension at the Curragh last month.

“It is disappointing to lose Frankie but one can understand where he is coming from,” Herbert continued. “If he thinks it is odds-against the horse running, he doesn’t want to be sitting around on Saturday not doing anything.

“We are now working on a replacement but have not made a decision at this stage. We will need to see who has got rides, who hasn’t got rides and who might be in Ireland anyway.”

Motivator’s participation depends on Bell considering the ground at Leopardstown being soft enough.

“Motivator’s run is in the lap of the Gods with regards to the weather, but a lot does depend on how they have watered,” said Herbert.

“Michael will go over tomorrow and have a look at the track, after which we will regroup.

“If the rain band that is due to arrive on Friday looks significant enough, we will probably have to send to the horse over and then just see how much rain arrives and what the track looks like on Saturday.”

Dettori was unable to confirm speculation he will ride hot favourite Scorpion in the Ladbrokes St Leger.

The latter is one of two intended runners in the final Classic of the season for Aidan O’Brien, who is also expected to saddle Oratorio in the Leopardstown race.

Stable jockey Kieren Fallon has yet to confirm where he will be at the weekend and Jamie Spencer has been booked for Avalon, O’Brien’s other Leger contender.

Speaking before racing at Leicester, Dettori said: “It looks increasingly unlikely Motivator will be running in Ireland on Saturday, so I would imagine I am going to be at Doncaster riding there.

“I don’t know anything about Scorpion, no-one has spoken to me about it.”