Hoof It, who had been a general 14-1 chance for the Diamond Jubilee Stakes at Royal Ascot, has been ruled out of the race by trainer Mick Easterby.
The five-year-old, who had finished fifth when favourite for the Duke Of York Stakes on his seasonal debut, will now be targeted at the Darley July Cup when he may belatedly meet Black Caviar.
Easterby said on Thursday: "Unfortunately Hoof It won't be running at Ascot. He is fine in himself but he looks a little dull in his coat and he isn't scoping very well.
"Looking back he might have had a slight infection when he ran at York.
"All being well we are hopeful he'll be able to take on Black Caviar in the July Cup."