Undefeated champion Songbird will be forced to miss the Kentucky Oaks on May 6, owner Rick Porter’s Fox Hill Farm announced Sunday evening.

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The farm’s Facebook page said the 3-year-old filly developed a low-grade fever after the Santa Anita Oaks on April 9 and has not been able to go to the track since.

Songbird would have been heavily favored for the 1 1/8-mile Oaks, considered the fillies’ Derby, at Churchill Downs. Many analysts have rated her the best 3-year-old of either gender, including the undefeated colt Nyquist, the Kentucky Derby favorite.