Italian jockey Frankie Dettori has been informed that he is facing an inquiry from French authorities following a "positive test".
While no details have been released as to what the 41-year-old has tested positive for, his solicitor has confirmed that it relates to a race in France in September.
"On behalf of Frankie Dettori I can confirm that as a consequence of a positive test at Longchamp on September 16 of this year, he will be the subject of inquiry by the medical committee of France Gallop next week," read a statement from his legal team.
"In compliance with and out of respect for the regulations of France Gallop he will not be commenting further until the procedures have been completed."
Dettori has ridden the winners of more than 500 Group races.