The Irish Derby winner dropped down to 10 furlongs for a competitive Juddmonte International at York but failed to cut any ice.
O’Brien had been contemplating taking on Winx in Australia but those plans were subsequently shelved after his eclipse on the Knavesmire.
“It was a mile and a quarter last time and he had options in Australia later in the year. We were not sure if he’s a horse who wanted 12 furlongs or whether he’d be better going back to 10. It was kind of a fact-finding mission,” said O’Brien.
“Obviously he had the easier option of going for the Voltigeur with a penalty but he didn’t run too badly in the Juddmonte and he probably was a bit positive in a race where you wanted to be settled a bit further back.
“He was staying on and obviously we’re stepping him back up in trip at Doncaster. He’s not from a stout family by any means but we’re quite hopeful he’ll get the trip.”
Of the dangers O’Brien said: “I suppose Kew Gardens had a great run in France and ran very well in the Voltigeur so he’s kind of the obvious one but the British team are always strong and I don’t think this year is any different.
“Obviously it’s a highly-competitive race but he’s an Irish Derby winner and he’s entitled to be in the line-up.
“I’d like to think Donnacha (O’Brien) will ride him, he’s riding very well and gave Latrobe a fantastic ride in the Irish Derby. He’s top class.”
O’Brien won the Melbourne Cup with Rekindling last year yet despite Latrobe being in the same Australian ownership, Latrobe is not certain to go.
“It’s a big ask for a three-year-old colt to go to Melbourne and it’s not a decision we’ll take lightly. Unless we’re very happy with him and he runs well in the Leger he might go but it is far from set in stone,” said O’Brien.
“He’s not very similar to Rekindling. Latrobe is a big, powerful horse and he doesn’t have the kind of stamina that Rekindling was assured of as he was from a stout family and had won over a mile-six before going there.”