(CNN) -- Jockey Frankie Dettori is facing an investigation after his lawyer confirmed he had given a "positive test" at a race meeting in France in September.
Dettori, who has won more than 500 group races during his long career in horse racing, issued a statement via his solicitor that confirmed a probe by France Galop.
The governing body of flat and jump racing in France conducted tests at the Longchamps course back in September, where Dettori was riding in trials ahead of the famous Prix de l'Arc de Triomphe meet in October.
A statement released by Dettori's legal representative, Christopher Stewart-Moore, said the 41-year-old would face an inquiry next week but did not specify what substance he is alleged to have taken.
"On behalf of Frankie Dettori I can confirm that, as a consequence of a positive test at Longchamps on 16th September 2012, he will be the subject of an inquiry by the Medical Committee of France Galop next week," it read.
"In compliance with, and out of respect for, the regulations of France Galop, he will not be commenting further until the France Galop procedures have been completed."
The Italian is one of horse racing's most famous names. He has won all five of Britain's "classic" races, including the Epsom Derby, as well as France's biggest race -- the Prix de l'Arc de Triomphe.
He has been champion jockey on three occasions since his debut in the late 1980s.
Arguably Dettori is most famous for riding seven different winners in one day at British racecourse Ascot in September 1996.
Recently it was announced he had left the Dubai-owned Godolphin stable after an 18-year spell and would ride as a freelance jockey in 2013.
Dettori has ridden 110 Group or Grade One winners for Godolphin since claiming the stable's first Classic on Balanchine in 1994.