Frankie Dettori has been replaced on two horses for trainers John and Thady Gosden at Newmarket on Saturday.
The Italian will be at the course to partner the Ralph Beckett-trained Lezoo, owned by his friend Marc Chan.
Dettori, 51, was criticised by John Gosden for his rides on Stradivarius and Saga at Royal Ascot last week.
"We're in the dark and searching for answers like everybody else," the jockey's manager Peter Burrell told the PA news agency.
Gosden helped get Dettori's career back on track following his split with Godolphin 10 years ago and the pair have enjoyed great success.
They have teamed up for big-race wins with the likes of Enable, Stradivarius, Golden Horn and Palace Pier.
But Dettori's name does not appear alongside Sunray Major and Stowell on Saturday's card, with the former partnered by James Doyle in the Criterion Stakes and Robert Havlin on the latter in the Fred Archer Stakes.
Dettori has ridden Sunray Major, owned by Juddmonte, in seven of his eight races and been aboard the Nat Rothschild-owned Stowell in his past five races.
Gosden was unhappy with Dettori after finishing third on Stradivarius, who was seeking a record-equalling third Gold Cup.
"Our hero overcomplicated matters," he said, and also suggested the jockey should have won the Britannia Handicap on runner-up Saga, owned by the Queen.
The Gosdens and Dettori have yet to comment on Saturday's Newmarket riding arrangements.
Some bookmakers reacted by offering odds on who would be their next stable jockey, with Hollie Doyle rated the favourite.
She won her first Classic race on Nashwa, for the Gosdens, in the French Oaks on Sunday.