Frankie Dettori will miss Saturday's Shergar Cup at Ascot to ride at Newmarket on the same afternoon.
Organisers of the event were hoping the popular Italian would be available to ride for the European team this weekend, but those hopes have been dashed as Dettori is required to ride for trainer John Gosden at Headquarters.
Dettori's agent, Ray Cochrane, said: "Frankie's going to Newmarket. John is going to have three runners there, including Princess Haya's filly in the Group Three (Pennywhistle, Sweet Solera Stakes). Hopefully Frankie will have seven rides. He can't be everywhere, I'm afraid."
In Dettori's absence, veteran French jockey Gerald Mosse will captain the European team in the Shergar Cup, Ascot confirmed.
Mosse is joined by German jockey Andrasch Starke and Swedish rider Per-Anders Graberg.
The Rest of the World team is made up of Yutaka Take, Corey Brown and Joao Moreira, while Fran Berry, Pat Cosgrave and Adam Kirby are the three riders representing the UK and Ireland.
The three jockeys riding for the girls team are Hayley Turner, Hollie Doyle and Josephine Gordon.