2000 Horse of the Year Tiznow sustained an injury during a workout last Friday, and a nuclear-imaging test conducted Monday revealed a problem with his lumbar vertebrae. "The prognosis is good, but we're going to have to walk him for 60 days before resuming training with him," said conditioner Jay Robbins Tuesday morning from his Santa Anita barn. The injury knocks Tiznow out of the May 12 Pimlico Special (gr. I).After what rider Chris McCarron called a "perfect" work Friday, Tiznow began blowing a lot and looked like he was cramping up back at the barn. Blood tests showed that he didn't tie up, but by Friday afternoon Robbins observed his star coming up short in the left hind while walking. Thus far in 2001, Tiznow has captured the Santa Anita Handicap (gr. I) and the grade II San Fernando Breeders' Cup Stakes, and finished second in the Strub Stakes (gr. II), all at Santa Anita.The son of Cee's Tizzy out of Cee's Song has won seven of 12 lifetime starts, including last year's Breeders' Cup Classic (gr. I), and has earned $3,445,950. He took home honors as 2000's champion 3-year-old male in addition to Horse of the Year. He did not run as a 2-year-old. Tiznow was bred in California by the late Cecilia Straub Rubens, and is owned by Michael Cooper and the Cecilia Straub Revocable Trust.