James Doyle is likely to sit out the action this weekend after he suffered an injury on the gallops on Friday morning.
Khalid Abdullah's retained rider banged a knee and has given up his rides at Chester.
Doyle's injury will be further assessed, with a view taken then as to whether he will ride the Sir Michael Stoute-trained Snow Sky in the Derby Trial at Lingfield on Saturday.
The jockey was also due to partner Border Legend at Lingfield and Sea Defence at Warwick's evening meeting on Saturday, but those mounts have already gone to Jim Crowley and Frankie Dettori respectively.
Abdullah's racing manager Teddy Grimthorpe said: "It's looking unlikely that James will be able to ride tomorrow.
"We have got someone in mind for Snow Sky but it is just not confirmed as yet."