Richard Johnson has landed the plum ride on Florida Pearl in the Hennessy Cognac Gold Cup at Leopardstown today.
The mount became available after regular jockey Ruby Walsh took a heavy fall at Naas on Saturday.
Walsh returned looking shaken but otherwise sound after Hollybank Buck had been brought down in the Kilwarden Handicap Hurdle but the jockey was later stood down for a week by the course doctor Matt Fay.
"Ruby is thought to have lost consciousness briefly after the fall and is stood down for the mandatory seven days.
"I have informed Dr Walter Halley (Turf Club medical officer) of the situation," said Dr Fay.
Florida Pearl's trainer Willie Mullins was at a wedding and missed the drama.
However, he said: "I've booked Richard Johnson as he seems to be the jockey in form at the moment.
"It's unfortunate for Ruby."
Dr Fay and the ambulance team had a hectic session with several riders being ferried to the local hospital throughout the afternoon.
Willie Slattery, whose mount Battery Park slipped up and brought down both Hollybank Buck and Charlie Swan's mount Jaguar Claw five out, suffered damaged ribs and facial abrasions.
The race went to Give Over who will bid to improve on his eighth place last year in the Ladbroke Casinos Hurdle Final at the Cheltenham Festival.
Walsh had earlier enjoyed a success on Killultagh Storm in the Opera Hat Beginners Chase in which David Casey was injured when the favourite Take Five crashed at the final fence when held.
Casey was stood down for the rest of the day but later pronounced himself fit to resume at Leopardstown tomorrow so long as he passes the course doctor.