O'Brien trains the current ante-post favourite for the 2000 Guineas in Camelot who was trading as low as ([2.82]) after Newmarket on May was announced as his target by the trainer.
Camelot was an impressive winner of last October's RP Trophy at Doncaster, his defeat of Zip Top and Fencing earning a Timeform master rating of 117P. The well-made son of Montjeu demonstrated an extraordinary turn of foot that day and, whilst his breeding may suggest Derby more than Guineas, he looks to have ample speed for the mile.
He has been ante-post favourite for both the Guineas and the Derby throughout the winter but with O'Brien also having Power and Nephrite for the first Classic of the season, his intended target had yet to be confirmed.
However, with Nephrite's shock defeat at the Curragh on Sunday meaning he has now been ruled out of the 2000 Guineas, it looks increasingly likely that Camelot will take his place in the line-up.
Power, available to back at ([16.0]), is said to be going the right way after a minor setback and could is already the winner of four of his six starts.
O'Brien also trains the current ante-post favourite for the 1000 Guineas, with Maybe trading as low as ([3.05]).
Maybe was the winner of all five of her outings last season, including the Group 1 Moyglare Stakes, and her Timeform master rating of 117p will likely make her the one to beat on May 6.
O'Brien has a total of 10 fillies left in the 1000 Guineas, including Group 2 Rockfel winner Wading, but her participation looks uncertain given the current Betfair market (available to back at [15.5]) and the Epsom Oaks could be the race for her.