Champion South Australian hoop Jason Holder has been suspended for five months having returned a positive reading to a banned substance.

The suspension, which will see him miss the rest of the 2021/22 racing season, came about from a sample taken at a random trackwork test at Morphettville in December.

Known as ‘Stubby' to the racing community, Holder has been charged with attempting to submit a substitute sample when asked to present for further testing at Racing SA's office on the same day.

The leading SA jockey pleaded guilty to both charges and was suspended for five months, with the ban reduced to that length of time from nine months.

His suspension could not have come at a worse time for Holder, who holds a narrow lead in the Adelaide Jockey Premiership.

Having ridden 27 winners so far in the metropolitan season, it leaves the door ajar for Barend Vorster (24) and Kayla Crowther (20) to stamp their claims as Adelaide's leading jockey.

With Group 1 races coming up thick and fast in both Melbourne and Sydney, Holder is set to miss out on a golden opportunity to further enhance his reputation.

Considering the ban will not end until late June, he is set to be sidelined for the Adelaide Racing Carnival beginning in late April, meaning he will miss out on a chance to add to his three Group 1 wins.