One-time champion Melbourne apprentice Jason Maskiell has been suspended from riding in races for 18 months after testing positive to a banned substance.

Maskiell fronted Racing Victoria stewards on Friday and pleaded guilty after providing a urine sample at Kyneton races on November 6 which contained a banned substance.

The substance was not named by stewards.

As part of the jockey's penalty, Maskiell is also suspended from riding trackwork or in barrier trials for a year and must provide written evidence of a satisfactory period of counselling before returning.

It's the second lengthy ban for Maskiell, Melbourne's leading apprentice in the 2009/10 season, after he was banned for six months in 2011 for testing positive to the drug ice.

Stewards back-dated Maskiell's latest suspension to November 10 which was the day he was stood down by stewards.

His ban from race riding runs until May 10, 2015.