Sprinter Sacre will not defend his Queen Mother Champion Chase crown at Cheltenham.
The Nicky Henderson-trained two-mile champion was pulled up at Kempton on December 27 and diagnosed as suffering from an irregular heartbeat.
Until then he had been undefeated over fences.
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 base on Saturday and the decision has been taken to miss Cheltenham and the rest of the season.
"He worked (on Saturday) as normal, but I just needed to see the old Sprinter back," Henderson told Press Association Sport.
"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.
"It's just not all there and I can't ask a horse of his standing, I can't sacrifice him. It's not what he's made of."
"At least he is sound and his heart is good, therefore there must be every chance he will be back next season 100 per cent and let's hope the old Sprinter is back in the Tingle Creek in December. That's what matters to us.
Paddy Power make the Gary Moore-trained Sire De Grugy, twice a Grade One winner this season, the new 5-4 favourite for the Queen Mother on March 12.