The Ballydoyle boss will run Diego Velazquez in Sunday’s Prix Du Jockey Club at Chantilly in France instead of the English Classic.
Diego Velazquez will go for the French Derby after coming back from a 197-day break with a strong fourth-place finish in the French 2000 Guineas at Longchamp earlier this month.
Sent off 17-1 he went down just a length to winner Metropolitan.
And he could see that form boosted massively if Roger Teal’s Dancing Gemini, who finished a half-length second at 26-1, runs a stormer in Saturday’s Derby.
O’Brien, who is chasing a record-extending tenth win in the Epsom Classic, will still saddle the two market leaders.
City Of Troy has been a stark drifter in recent days but Coolmore allayed any injury fears with a new video of him galloping at home.
While Los Angeles has come in for a surge of support and is 3-1 joint-favourite for the £1.5m race with some bookies.
O’Brien will also saddle £2m purchase Euphoric, who was beaten a length by Los Angeles when last seen in a Leopardstown Group 3 earlier this month.
Speaking of his decision to run Diego Velazquez in France, O’Brien said: “We were very happy with the run in the French Guineas.
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“We always thought he would run a very nice race and we always thought the step up to mile and a quarter would suit him well.
“We were delighted to go to Longchamp because it is obviously right-handed like Chantilly.
“We felt these two races would suit him well and we were very happy with the way he came out of the French Guineas and happy with everything he has done since.
“He is a very good mover so the better the ground, the better it would suit him.
“We thought he would probably want good, fast ground as you can see when you see him gallop he has a very low, long action.
“Hopefully the ground won’t be soft and will improve before Sunday.
“Definitely the better the ground, the better his chance.”
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