Melbourne Cup-winning jockey Michelle Payne is under investigation after she allegedly registered a positive test for a banned substance.

Racing Victoria stewards said they would hold an inquiry into the results of a sample from Payne which confirmed the presence of Phentermine, an appetite suppressant.

The sample was taken after the Swan Hill Cup meeting on June 11.

Payne will face the inquiry tomorrow.

She has been stood down from riding in races and trackwork.

Payne shot to fame in 2015 after becoming the first female jockey to win the Melbourne Cup, riding 100-1 outsider Prince of Penzance to victory.

She revealed last year that moving into training was the next step in her career, and that her personal goal was to both train and ride a Melbourne Cup winner.

At the Swan Hill Cup meeting, Payne rode and trained two horses — Our Zariah, which came 10th in a 1,600m maiden race, and Sovereign Wealth, which came third in another maiden over 1,600m.