Dettori will miss the ride after receiving a nine-day careless riding ban at Royal Ascot last month and that suspension will also rule him out of riding Emily Upjohn in the Coral-Eclipse on Saturday.
Murphy has never ridden Chaldean in public before but Barry Mahon, racing manager for Juddmonte, the owners of the top-notch colt, said once the Irishman was available to replace Dettori, connections were left with a straightforward decision.
“If everything is going okay with the horse and Andrew [Balding, trainer] is happy with him, the plan will hopefully be to run at Deauville and, as far as I am aware, Oisin Murphy will take the ride,” Mahon told the Nick Luck Daily Podcast.
He added, “Oisin is a top-class jockey and is part of Andrew's stable and we'll be delighted to have him on board. [Chaldean is] good, he came out of Ascot in great form and has only had two runs this year so is relatively fresh and he's in good shape.”