Azertyuiop, who once looked the most likely successor to the great Moscow Flyer, has been retired after failing to make a full recovery from injury.
The nine-year-old missed all of last season after striking into himself when second in the Celebration Chase at Sandown in April 2005.
Trainer Paul Nicholls and owner John Hales had hoped Azertyuiop would be fit to return this campaign but after seeking veterinary advice, he has been retired.
Hales told the Racing Post: "It's sad news but it's also a relief because he would not have been able to perform to the level he showed before his injury."
Azertyuiop won 11 of his 22 starts over fences including the 2003 Arkle Trophy at Cheltenham, as well as the Queen Mother Champion Chase the following season.
Nicholls added: "I was not exactly happy with the horse over the past couple of days due to the fact he did not look as if he would stand training this autumn.
"I actually sent him back to John's so that his vet could reassess the problem, and everybody has come to the same conclusion - that the best thing to do for the horse was retire him."
