Guarantee condition critical
Guarantee is in a "critical" condition after he sustained a bad injury at Chester on Saturday.
The William Haggas-trained four-year-old was pulled up two furlongs out in the Golden Square Shopping Centre Chester Handicap.
Owners Highclere Thoroughbred Racing tweeted: "Guarantee suffered a major tendon injury yesterday and was taken back to Newmarket. His condition is critical and we are all very concerned."
Guarantee won the Melrose Stakes at York last season and finished seventh on his penultimate start in the Betfred Ebor.
Haggas said: "It's not very good, I'm afraid.
"He's ruptured his superficial flexor tendon. His career is definitely over."