Frankie Dettori will ride Tattersalls Musidora winner Snowfall in the Cazoo Oaks at Epsom on Friday.
Stable jockey Ryan Moore has opted to partner favourite and QIPCO 1000 Guineas fourth Santa Barbara leaving the Italian, who has won the Classic five times previously, to step in aboard her stablemate.
They are part of a five-strong raiding party from the yard with Seamie Heffernan on Divinely, Wayne Lordan aboard Willow and William Buick on La Jaconde.
Dettori has developed a successful partnership with O'Brien in recent seasons, winning the QIPCO 1000 Guineas this season aboard Mother Earth.
He is expected to pick up the ride on High Definition in the Cazoo Derby for the stable too if, as expected, Moore chooses favourite Bolshoi Ballet.