Paul Nicholls reacted angrily to calls for Kauto Star to be retired after he was beaten in the King George VI Chase on Saturday.
The 11-year-old was bidding to make history at Kempton by becoming the first horse to win the prestigious contest five times.
But having made a couple of jumping errors, the legendary performer had to settle for third behind impressive winner Long Run, leading some observers to believe the French-bred star was past his best.
Nicholls subsequently said his charge had suffered a small bleed after the race, while blood test results have also revealed he has developed a low-grade infection.
"I have read some complete nonsense in the last few days from people who don't know the horse. They would be far better off keeping quiet and leaving it to people who know the horse to make the decision,"
Nicholls told Racing UK.
"It puts a lot of pressure on me and if I think he's not performing or going well, then I'll say so.
"But up until Saturday, you wouldn't know he was any different to what he's ever been.
"He loves what he's doing. If he's retired, what's he going to do?
"He's in good order and we'll retire him when we feel it's right.
"If he runs in the Gold Cup this year and runs disappointingly, then perhaps we'll think about it.
"I'll do the best thing for Kauto and if we have any inclination that he's on a downward scale or he's not enjoying it, of course we'll call it a day.
"He might not win the Gold Cup, but I'm sure he'll run a good race if we get him back to his best.
"I'm actually glad we have a few little reasons. He had the little bleed and now his blood has shown he wasn't quite at his best.
"I think you'll find he was beaten by a very good young horse and, at
the end of the day, if he hadn't made the mistake trying his damnedest
to get back into the race, he'd have been second."
Since his Kempton reverse, criticism has also been levelled at champion
jockey Tony McCoy, who was riding Kauto Star for the first time.
Nicholls would have preferred to have had the injured Ruby Walsh in the saddle, but insists his absence did not effect the result.
"Ruby riding him is a big advantage because he's ridden him all his career and if you take that advantage away, no matter who is riding him, the advantage has gone," Nicholls added.
"AP gave him a great ride on Saturday. He'd never ridden him before in a race, so he was going into it blind a little bit, but he wouldn't have won on Saturday with Ruby or anybody riding him.
"It was obviously difficult for AP having never ridden him before."
Despite having won the King George so impressively on four previous occasions, Nicholls claims Kempton is no longer Kauto Star's ideal track.
"He's better round Cheltenham, which is more of a galloping track and more of a staying track," he added.
"He's won two Gold Cups round Cheltenham and he only won the King George the year before by so far because they went too fast and he just outstayed them.
"He may have lost a little bit of speed, in which case Kempton won't
suit him now."