O’Brien , who won last year’s renewal with Galileo, has both Bach and Della Francesca entered for the mile and a half contest but neither is certain to run.
Should he run at the Berkshire track Bach, who was second behind Rebelline in the Tattersalls Gold Cup at the Curragh earlier this year, would be tackling the mile and a half trip for the first time after showing much of his best form over shorter distances.
Della Francesca, whose best run came when winning the Group Three Gallinule Stakes at Leoparstown, has already run over this longer trip when a nine-length sixth behind High Chaparral in the Budweiser Irish Derby.
The pair also hold alternative engagements closer to home in the Group Three Meld Stakes at the Curragh on the same day.
The ground at the Curragh is currently yielding but officials are hoping to be able to offer good to yielding ground, which could see O’Brien reroute his pair there instead.
The champion trainer said: ‘‘They are both good ground horses and that will be a factor as to whether they go to Ascot or stay at home for the Curragh.’’
Bach is currently a 33-1 shot with William Hill for the event while Della Francesca is available at 40-1.
Watering continued yesterday ahead of the three-day meeting as the course enjoyed a drier, sunnier day than forecast.
Clerk of the course Nick Cheyne is aiming to produce going no faster than good to firm for the two-day fixture, which gets under way on Saturday.
He said: ‘‘It remains good to firm. We have been watering yesterday and today.
‘‘We were forecast some rain for today but that has not materialised. The forecast for tomorrow is for a warm, bright day but there might be some light rain on Thursday morning.”
The lack of rain has seen the bookmakers reporting some significant support for Godolphin’s Grandera.
The four-year-old has hardened to 11-8 favourite with William Hill today from 6-4, while stablemate and former favourite Sakhee is now 2-1 second choice.
Godolphin representatives are due to work the Ascot track today to see if the ground will be suitable for Sakhee to run.
Hills’ have also clipped Sir Michael Stoute’s Golan to 7-1 from 8s while Zindabad has shortened to 8-1 from 12-1 with the firm.
Meanwhile Peruvian Chief is set to tackle the Hong Kong Jockey Club Sprint at Ascot on Sunday after being given the all clear by his owners.
Connections of the Nick Littmoden-trained five-year-old had been mulling over their options after the gelding finished a neck second to Brave Burt in the Doubleprint Handicap at Ascot earlier this month.
Littmoden had been aiming his charge at the Vodafone Stewards’ Cup at next week’s Glorious Goodwood meeting, but the son of Foxhound is now set to run at Ascot too.
The trainer said: ‘‘The owners have decided to run him in both the Ascot race and the Stewards’ Cup. They will be his final two races over here this season and then he will be coming to Dubai with me for the winter.
‘‘He’s really well, very well indeed. He’s in good form and take his racing well so that’s why we can take both races in.’’
The Ascot sprint is over five furlongs while the Stewards’ Cup is a furlong longer.
Peruvian Chief has performer creditably over both trips before now and Littmoden is not unduly worried about asking his horse to move up in distance.
‘‘The stiff five furlongs at Ascot really suits him and he’s run well there a couple of times but he was also second in the Stewards’ Cup consolation race at Goodwood last year so both trips seem to suit him well,’’ he explained.
‘‘We would definitely want the ground to be on the fast side though.’’
Marcus Tregoning has earmarked the Geoffrey Freer Stakes at Newbury as the next target for Mubtaker following the horse’s brave effort to beat all but Millinery on his belated return to action at the Newmarket July meeting.
Angus Gold, racing manager to Mubtaker’s owner Hamdan Al Maktoum, said: ‘‘We’re keen to win a couple of group races with him rather than pitch him in against the very best, which is why we shied away from the King George.
‘‘He was only just ready for the Princess of Wales’s Stakes and Marcus tells me he’s in sparking form and taken his race well.
‘‘The plan is to run him in the Geoffrey Freer next and hopefully, he can then enjoy a fruitful second half of the campaign.’’
Lord Weinstock, owner of Golan and Pilsudski, died yesterday aged 77. The leading owner, a former top industrialist, had horses with Michael Stoute, Marcus Tregoning and Nicky Henderson in Britain, as well as owning the Ballymacoll Stud Farm in County Meath.