Annie Power has been ruled out of her scheduled return in the Bar One Racing Hatton's Grace Hurdle at Fairyhouse on Sundays.
The Willie Mullins-trained mare, who only lost her unbeaten record in the World Hurdle at the Cheltenham Festival, had been declared for the Grade One on Friday morning but is now lame.
Jockey Ruby Walsh will instead ride stablemate Zaidpour, also owned by RIch Ricci.
Mullins' son and assistant, Patrick, said: "These things happen unfortunately.
"I don't think it's serious, we hope not anyway.
"Zaidpour is a good substitute to have in any case.
"He's won the race before and has won the Royal Bond at this meeting so he obviously goes well at the track and at this time of year."
In Annie Power's absence, Jessica Harrington's Jetson would appear to have leading claims.
He was last seen shocking Quevega at Punchestown, after which the star mare was retired.
While Harrington fears the nine-year-old now saves his best for the spring, this has always been his target.
"It's exciting to have him back in action," she said.
"He caused a bit of a shock by beating Quevega and whether she was quite at her best that day, who knows?
"He's in good form and is ready to run. He has very limited opportunities now as he's out of handicaps and he'd have to carry a Grade One penalty in other races.
"We'll have to pick and choose his races carefully, but I just think he's a spring horse anyway - he always comes to himself at that time of year.
"After this he'll go to Leopardstown at Christmas for the three-miler, but it's all about the (spring) festivals with him.
"He's run well at Cheltenham, Aintree and Punchestown for the last few years."
Prolific mare Little King Robin takes her chance after a fine third to two-mile kings Hurricane Fly and Jezki in the Morgiana Hurdle at Punchestown, with the field completed by Lieutenant Colonel and King Of The Picts.
