After the latest of three disappointing runs, his trainer Mike Moroney has revealed the four-year-old will not be racing again as a colt.
The three-year-old filly returns to the scene of her Prix Morny victory last year, having been awarded the Commonwealth Cup in the stewards room.
Holders of slots in the A$15 million (£8m) Sydney sprint have sounded out David Ward about the challenge, which is being given careful consideration.
The four-year-old colt was favourite for the Diamond Jubilee Stakes only to be scratched after heavy rain at Ascot turned the ground soft.
Tom Marquand was first choice for the up and coming Ed Walker-trained sprinter but Murphy will have the mount as Marquand is required to ride Nahaarr.
Stradivarius takes a key step on his path to the Prix de l’Arc de Triomphe in the Prix Foy under Frankie Dettori at ParisLongchamp.
Ed Walker is considering options for Derby fifth English King with the King George VI and Queen Elizabeth Stakes not ruled out.
Ed Walker said it would be “a sin” to leave Frankie Dettori in the weighing room as he expanded on the decision to take regular partner Tom Marquand off the Investec Derby favourite English King.