Clive Brittain's filly has been denied a run in the Irish Classic after she suffered a setback at her Newmarket home yesterday morning.
Brittain said: "It's heartbreaking, but it's what the game is all about. You have your good days, and you have your bad days. She'd done all her major work six days ago, and was only having a blow-out. The girl who looks after her was very happy with her, as always.
"But an hour later, after the horse had a wash-down, we found a bit of blood coming out of her near-side nostril. It was only a trickle, but if there is in any doubt, we always take them out. It could be something over nothing, but you can't take any risks.The filly is still bright-eyed and alert. I don't think we've a sick animal on our hands."
Rizeena won the Group One Moyglare Stud Stakes on her last visit to The Curragh, but only finished seventh behind Miss France on her seasonal bow in the English equivalent race.
Meanwhile, Kingman will face 13 opponents when he gets a second shot at Classic glory in the Tattersalls Irish 2000 Guineas at the same venue tomorrow.
John Gosden's exciting colt was a hot favourite to secure his fourth win from as many starts in the 2000 Guineas at Newmarket at the start of the month, but was narrowly beaten on the Rowley Mile by the Richard Hannon-trained Night Of Thunder.
With his conqueror not making the trip to Ireland this weekend, Kingman is odds-on to take the Irish version back to Newmarket.
Despite Night Of Thunder's non-participation, the Hannon team still saddle a major contender in Shifting Power, who was not beaten far into fourth at Newmarket.
Dermot Weld has made a fantastic start to the season and relies upon Amethyst Stakes winner Mustajeeb, after deciding against running Tetrarch Stakes scorer Alkasser.
Aidan O'Brien is unsurprisingly mob-handed, with War Command, a disappointing ninth in the Newmarket Guineas, joined by stable companions Great White Eagle, Michaelmas, Johann Strauss and Fountain Of Youth.
Obliterator, Big Time, Prince Of All, Dolce N Karama, Mandatario and Davids Park also feature in the Classic field. Along with Alkasser, the only other withdrawal from the latest entry stage was Deegan's Shining Emerald.