After fielding six of the 12 entries at the five-day stage for Saturday’s Doncaster spectacular, O’Brien plans to whittle his raiding party down to a quartet headed by ante-post favourite Honolulu.
Johnny Murtagh is pencilled in for the ride on the Ebor runner-up, with Christophe Soumillon possible for Great Voltigeur third Macarthur, Mick Kinane down for Mahler and Seamie Heffernan or Colm O’Donoghue on Acapulco.
O’Brien, who most recently scored with Scorpion two years ago, said: “We think Honolulu has improved with every run.
“He won a Listed race before the Ebor and he is progressing. We have been pleased with him since York.
“Mahler had a busy time before Ascot so had a break and we used the Voltigeur (where he was fifth) as a prep race – we were very happy with him.
“He has really come forward since then, he handles fast ground and he stays really well.
“Macarthur came back sore from the Derrinstown so we gave him a break and he was off a long time before the Voltigeur.
“He has come forward for that and is a good-moving horse who handles fast ground.
“We were always confident it would happen with him and we have given him time to progress.
“Acapulco is another to have had a break after the Derby. He has come on since the Voltigeur (fourth) and is a horse who will get the trip well.”
Irish Derby winner Soldier Of Fortune was left in the race but is all set to head to France at the weekend for an Arc trial.
O’Brien said: “The plan is to take him to France on Sunday. Circumstances can change and the Leger is there as an option, but the plan is to go to France.”
John Gosden, successful with Shantou 11 years ago, will almost certainly be double-handed after deciding that Voltigeur winner Lucarno will probably take his place alongside stablemate Raincoat.
Speaking from the Keeneland Sales, Gosden said: “I think it is likely he (Lucarno) will run, but I need to have a look at the way the race is shaping up.
“He worked nicely under Jimmy Fortune on Saturday morning and I am very happy with him. He has come on nicely since the Voltigeur.
“The extended trip is an issue which is why we have been hesitant about running.
“However, the track and the ground will suit but we will be going into no-man’s land in the final two and a half furlongs.”
He added of Gordon Stakes third Raincoat: “It was a silly race last time as they sprinted at the finish but the trip will suit him well and he has plenty of stamina.”
Following his impressive victory over the Leger trip at Haydock on Saturday, Regal Flush has been supplemented to the field by Sir Michael Stoute at a cost of £40,000.
Stoute, who has saddled the Leger runner-up on five occasions but is still chasing his first victory, said: “I felt after his convincing victory on Saturday and the way he has progressed so nicely of late that it was worthwhile.”