Steven Pateman, the champion jumps jockey who has also turned his hand to training, has been charged over an elevated cobalt reading returned by one of his runners before a steeplechase.
Pateman and stable employee Jessica Barton were hit with charges by Racing Victoria stewards on Thursday.
The Pateman-trained Sir Walter Scott was tested before running in the Great Western Steeplechase (3800m) at Coleraine on September 24 last year, with two laboratories confirming the presence of cobalt at a level greater than 200 micrograms per litre in urine.
Cobalt is considered a prohibited substance above 100mcg/L.
Pateman and Barton have both been charged with administering, or causing to be administered, a prohibited substance for the purpose of affecting the performance or behaviour of the horse in a race.
The pair also face an alternative charge of administering, or causing to be administered, a prohibited substance which was detected in a race day sample, while Pateman faces a third charge in the alternative of presenting a horse to race when a prohibited substance was detected.
A date for the Racing Appeals and Disciplinary Board to hear the case has yet to be determined.