Trainer Sir Michael Stoute expects the Queen's horse, Estimate, to "run very well" in her attempt to retain the Gold Cup at Royal Ascot on 19 June despite not having had a prep race.
The Queen last year became the first reigning monarch to own the winner of the showpiece.
However, Estimate has run only once since because of a muscle injury.
The mare - also a winner at Royal Ascot in 2012 - finished down the field in a race on Champions Day in October.
Stoute said: "She's not been straightforward. She's had a muscle problem in her right hind [leg], and that's why she hasn't had a prep run.
"She's made some progress in the last month. The Gold Cup's a tough assignment this year, but I expect her to run very well."
Estimate is currently third favourite for the £375,000 prize, behind last year's St Leger winner Leading Light and in-form Brown Panther, partly owned by Michael Owen.
Meanwhile the racecourse is being irrigated for the first time since August ahead of next week's Royal Ascot meeting. The going is currently good, good to firm in places.
Clerk of the course Chris Stickels said: "The forecast is fairly settled - dry and warm - now until at least Thursday of next week.
"The watering started yesterday and we put 10mm on the straight course and 4mm on the round. We aim to have conditions the same as now for the start of the Royal meeting on Tuesday."