Chief Dan George is to miss the Coral Scottish Grand National on Saturday following an unsatisfactory blood test.
Jimmy Moffatt's stable star was a leading fancy for the Ayr marathon in which he was fifth last year thanks to his win in the William Hill Trophy Handicap Chase at the Cheltenham Festival.
He also held an entry in the bet365 Gold Cup at Sandown the following weekend.
"We made a decision between Maurice (Chapman, owner), myself, Paddy (Aspell, jockey) and my father this morning. We took a blood test on him last night and his blood is not quite up to the standard we would want," said the Cartmel trainer.
"We have decided to put him out in a field and look forward to next season with some relish.
"He's done us proud this year and we don't want to take any chances with him at all."
Chief Dan George just missed the cut for the John Smith's Grand National in which he was 12lb well in, and Moffatt is already looking ahead to next season.
"You'll probably see the horse again in the Charlie Hall Chase. That will be his starting point," he went on.
"He'll be out in a field in a fortnight to three weeks.
"There's nothing wrong with the horse, he's fine. It's just that his blood is not quite right.
"It's disappointing but at the same time my owners are very good and the horses always come first.
"Next year the world is our oyster. He is going the right way, he is on an upward curve. We don't want to do anything that is of any risk to the horse at all.
"It's nice to put a Cheltenham winner out in the field."
