Trainer Nicky Henderson says star chaser Altior is extremely unlikely to run in the King George at Kempton after failing to fully convince connections during his latest work-out.

Earlier this year, Henderson earmarked the Boxing Day showpiece as the main objective for the dual Queen Mother Champion Chase winner.

But doubts arose when Altior suffered his first defeat in 20 starts over obstacles when unable to reel in the Paul Nicholls-trained Cyrname in a highly anticipated clash at Ascot last month.

Henderson was keen to let the dust settle, but confirmed after Saturday's hit-out he and jockey Nico de Boinville were not 100 per cent satisfied with the results.

"It wasn't as if he didn't work well," Henderson said.

"It was very satisfactory as he worked with two very good horses. Nico just said he felt a little bit flat and he didn't have his normal mojo.

"I've spoken to (owner) Pat Pugh. We are really saying the King George is extremely unlikely.

"He is not out, but it is unlikely. Nothing is certain in racing and in life, but that is where we stand at the moment."

Henderson would not be drawn on whether Altior could still step up to three miles (4800m) at some stage, or revert to the two-miles over which he has enjoyed such phenomenal success.

"He had a very hard race and was very tired after the race at Ascot. We don't want to put him into another fierce battle as we might undo everything," Henderson said.

"Me and the owners have got to look after the horse as he is the most important part of the equation."