Two-time winner Tiger Roll has been ruled out of this year's Aintree Grand National after being given a handicap mark of 161.
It would mean the horse would have to carry a weight of at least 11-stone 4-pounds in April, which could rise if horses above withdraw from the race.
Michael O'Leary has blasted this decision while speaking to the Racing Post.
"This rating is absurd, and unfair on a 12-year-old chaser.
"It is a pity that the handicapper won't give Tiger Roll either a fair rating, or a fair weight in the Aintree Grand National, where he could at least try to emulate Red Rum's three Grand National wins.
"However, the handicapper sets the weights, and even if he is manifestly wrong in the case of Tiger Roll, there is nothing we can do about it other than remove him from the race, since we don't believe it is safe or fair to ask him to carry close to top weight at the age of 12.
"Since we are responsible for the welfare of Tiger Roll, we must protect him from the idiotic opinion of this handicapper.
"We therefore regret to announce that he will not run in this year's Grand National.
"Instead Tiger Roll will be trained for the Cross Country race at Cheltenham, and there is every likelihood that win, lose or draw, this will be his last racecourse appearance."
The 12-year-old would have been chasing a record-equalling third win at Aintree.
Red Rum won the prestigious race in 1973, 1974 and 1977.