Sprinter Sacre will not defend his Queen Mother Champion Chase crown at Cheltenham next month.
The Nicky Henderson-trained two-mile king was sensationally pulled up at Kempton on 27 December, where he was quickly diagnosed as suffering from an irregular heartbeat.
That problem righted itself, and he has been closely monitored since by equine specialist Celia Marr, steadily pleasing his team and with a racecourse gallop in the offing.
However, the eight-year-old did not show his usual brilliance in a piece of work at Henderson's Seven Barrows base on Saturday, and the decision has been taken to miss Cheltenham and the rest of the season.
Henderson said: "He worked (on Saturday) as normal, but I just needed to see the old Sprinter back yesterday. Everything had been going very well, his work was building up. It had been OK, but I was looking for that something he shows, he is extraordinary and always used to give us that at home.
"I talked extensively with Caroline and Raymond Mould, who have been very understanding.
"I said the other week it was 50-50 (getting to Cheltenham) but quietly I thought it was above that, I honestly thought we were going the right way.
"It's just not all there and I can't ask a horse of his standing, I can't sacrifice him, I think it is fairer to everybody - the horse told us what he wanted to tell us yesterday. It's not what he's made of."