Michael, one of Britain’s top show jumpers, was suspended from riding in international competition by the International Equestrian Federation (FEI) on 26 June.
The suspension was put in place after traces of the hormone altrenogest — found in Regumate — were found in a sample taken from the stallion Tackeray at a show La Baule on 14 May.
Regumate is a preparation that can legally be given to mares but not to stallions — on which it also has a calming effect.
Michael has not requested a second sample — the B sample — be tested, and blames the positive test on a mix-up in feed buckets as he has mares that compete on Regumate.
The FEI disciplinary tribunal hearing will take place in London, but is not open to the public.
FEI spokesman Malina Gueorguiev said: “We don’t expect to have a decision until about two or three weeks after the hearing.”