Although Tickity Bleue dead-heated on New Year's Eve and Kumbeshwar was a respectable third in the Fairlawne Handicap Chase at Cheltenham on Wednesday, Barbury Castle has been very quiet after a good start to the season proper.
"We have had only two winners since December 3 and while I have never been more delighted to get a dead-heat than I was at Warwick, the horses are clearly not right, so it is time to stop," King told www.alankingracing.co.uk.
"Some horses have had inflammation in their lungs and we must get to the bottom of the problem.
"It's a shame as we had made our best start to a season, and the horses were in terrific form in October and November, but a few alarm bells started to ring during Hennessy week and, though, Invictus apart, that was another good weekend, we have had precious little to celebrate since.
"It is frustrating, but we need to be patient and do the right thing by the horses, so until they come right again it is best to take a pull.
"Maybe a few years ago I would not have handled a similar situation so well and would have soldiered on, but you learn by experience and if the they are not right you have to be very careful.
"The worst thing you can do is to run your horses when they might be carrying something - that could well mean losing the horse for later in the year when most of the big Festivals are run."
King's Champion Hurdle hope Grumeti was one of the notable disappointments over the period and he said: "Grumeti's scope on the Monday before the Christmas Hurdle was good, but he ran no sort of race at Kempton and was beaten with half a mile still to run.
"He blew very hard afterwards and came back wrong, so he is on antibiotics, but it just goes to show how hard it is to judge whether a horse is right or not before you run them.
"Before Kempton Grumeti was showing all the right signs, so it is very difficult, but we will give him a bit of time now and if he comes right in time we could go for something like the Kingwell Hurdle at Wincanton in February."