Three-time Coronation Cup hero St Nicholas Abbey will bypass Royal Ascot and instead be targeted at the King George VI & Queen Elizabeth Stakes at the same track in July.
The hugely talented six-year-old clinched the sixth Group One prize of his career with a superb performance on Epsom Derby day last weekend, after which connections mentioned Royal Ascot's Hardwicke Stakes as a possible next port of call.
But, the son of Montjeu will instead aim to secure further top-level honours in the King George, having finished a close third last season.
O'Brien said: "St Nicholas Abbey has come out of the race at Epsom really well and we're looking forward to his next run."
But O'Brien is expecting impressive Irish 2000 Guineas scorer Magician to be part of the Royal Ascot team.