The Irish trainer admitted slight concern about the six-year-old but hoped the problem would be successfully treated.
“Since he arrived here, all four of his legs were a bit humid, which is because he didn’t get to do much walking,” said the Ballydoyle handler.
“We will treat it and hope it disappears quickly.”
Starspangledbanner has had four races in the last few months since returning from an unsuccessful stud career.
O’Brien was heartened by the Australian bred’s run at Dundalk last week when he was a close fourth in a Listed race.
“We learned very early on that he hates soft ground,” he said.
“When he was trained in Australia, he was getting away with being ridden in front and then being slowed down, but you can’t do that in America.
“We learned after France (Prix de la Foret), that he’s a sprinter who wants a strongly-run six furlongs and this was the only big sprint left for him.
“We made plenty of use of him at Dundalk the other night and he pleased us.”
Meanwhile, connections of Sky Lantern believe the two-year-old is “a worthy favourite” for the Breeders’ Cup Juvenile Fillies Turf at Santa Anita tomorrow.
Richard Hannon’s charge, winner of the Moyglare Stud Stakes at the Curragh in September, showed her well-being in a routine workout under stable jockey Richard Hughes on the dirt surface.
The trainer’s son and assistant, Richard Hannon jnr, said: “I think she’s a worthy favourite and has a favourite’s chance.
“We’re happy with the draw (three) and Hughesie will try to ride her handily and see how we come out of the first bend – I will leave it to him.
“For me, they’ve all got her to beat.
“I would say she’s the best chance we’ve had of winning at the Breeders’ Cup.”
lNavan maiden winner Loch Garman takes a huge jump in class for the Group One Criterium International at Saint-Cloud today.
The son of Teofilo only made his debut a week ago but ran out an impressive winner in testing conditions, which bodes well ahead of his French assignment.
Kevin Manning will partner the Jim Bolger-trained youngster.
Bolger said: “It’s his last chance (to run this year), so that is why we’re running him back so soon.
“He handled the softer ground in Navan, so we’re hoping for the best.”
Asked whether he considered the colt a Derby prospect, the trainer said: “I’m not sure, I don’t think so.
“He might not get a mile and a half.
“He gets a mile well. He’s a nice type.”
Loch Garman faces just five rivals over a mile, with Ralph Beckett’s maiden Anna’s Pearl the sole British representative.
Johnny Murtagh rides Pearl Flute, while US Law, Triple Threat and Kenhope complete the line-up.