Racing Victoria stewards have opened an investigation into a positive swab taken from a runner prepared by young trainer Logan McGill.

McGill’s charge Arapahoe Moon produced a positive test to Dexamethasone, a short-acting corticosteroid, in a pre-race sample taken at Avoca on Anzac Day.

Arapahoe Moon finished sixth of 10 as a $20 chance in the race.

Stewards advised McGill of the findings earlier this month before confirming the results of a second test on Wednesday.

The investigation is continuing.

Recent cases involving Dexamethasone had resulted in fines for trainers charged.