Aidan O'Brien has raised concerns over the fitness of double Derby winner Australia before Wednesday's Juddmonte International at York.
Australia, who has not run since his victory at the Curragh, is set for his first open-age race at York.
"I suppose, because he has done so well, we are a little bit worried about his fitness," trainer O'Brien said.
"But really, when you give a horse a break - especially a three-year-old - going into the autumn, you want him to do well. He did well, he did very well."
Irish champion trainer O'Brien's comments suggest his focus is on building up Australia's fitness for later races following his post-Irish Derby break - although the horse is still odds-on favourite with all major bookmakers.
The 44-year-old said before the Epsom Derby that Australia - son of his 2001 Derby winner Galileo and 2004 Epsom Oaks champion Ouija Board - was the best horse he had trained.
The colt, who has ridden six races to date, was beaten into third place in the 2000 Guineas in May - his first outing of the year - as Night Of Thunder finished first and Kingman second.
|Australia's race record|
|30 June: Barronstown Stud Maiden (Curragh, Ire) - 2nd||3 May: 2000 Guineas (Newmarket, Eng) - 3rd|
|20 July: Darley Maiden (Curragh, Ire) - 1st||7 June: Epsom Derby (Epsom, Eng) - 1st|
|7 Sep: Breeders Cup Juvenile Turf Trial Stakes (Leopardstown, Ire) - 1st||28 June: Irish Derby (Curragh, Ire) - 1st|
His two high-profile victories since then have secured his status as the leading three-year-old over middle distances.
O'Brien's son Joseph, who has ridden Australia for all six of his outings, will continue in the saddle, and is slimming down to 8st 12lbs for the race, having not ridden under 9st this year.
Despite the fact the Juddmonte is an open-age race, only two horses older than Australia are in the field.
Telescope, trained by Sir Michael Stoute, finished second in the King George VI and Queen Elizabeth Stakes at Ascot on 26 July, while William Haggas's horse Mukhadram finished third in that race.
Mukhadram had previously claimed a first Group One victory in Sandown's Coral-Eclipse on 5 July, while Telescope won the Hardwicke Stakes by seven lengths at Royal Ascot in June.
Kevin Ryan's French Derby winner The Grey Gatsby is a contender, returning to the scene of his victory in the Dante Stakes earlier in the year.
Peter Chapple-Hyam's Arod has ground to make up on Australia on Epsom form, but is expected to be more effective over a mile and a quarter.
Australia's stable companion Kingfisher completes the field.