Nicky Henderson has been forced to rule Sprinter Sacre out of his intended comeback in the BetVictor Tingle Creek Chase at Sandown on Saturday.
The star of the National Hunt scene returned a dirty tracheal wash earlier in the week and his results are still not 100% leaving the champion trainer to take the agonising decision not declare his stable star.
Henderson said; "We've taken the decision not to run. We've re-tested him and just got the results back.
"Having spoken to all the vets possible and his owner Caroline Mould, we've decided not to go.
"His figures have improved quite dramatically since Monday but there was just one figure that was causing us concern."
Henderson added: "I had a figure in my mind that I wanted to see today and it just wasn't quite there.
"We can't take any chances with him and having told everyone earlier in the week that he had a problem and if we ran him and god forbid something happened, then everyone would ask what we are doing running him.
"I suppose there's the Desert Orchid Chase at Kempton but we'll probably wait for the Victor Chandler Chase now.
"Now we can get him on some medication and it is the sort of thing that will clear up in no time but obviously we couldn't give him anything earlier in the week.
"Nico De Boinville rides him everyday and having ridden him this morning he said he still looks and feels fantastic and that he was in tip-top form and that you could never tell externally that there was a little something a miss.
"However, sadly we'll have to bypass the weekend. It's marginal and we'd always wanted to start here but we'll have to make a new plan.
"It's very disappointing for everybody but Captain Conan will take his place and he's a horse on the upgrade."