Star Brisbane apprentice Luke Tarrant has been stood down indefinitely following an irregularity in a random drug test.

Chief steward Alan Reardon said Tarrant the irregularity was detected in a sample taken at Ipswich earlier this month.

"He is stood down pending an inquiry to be held next month," Reardon said.

It means Tarrant will not be able to ride at the Gold Coast feature meeting on Saturday.

It is the latest in a series of setbacks for Tarrant.

Last month he was disqualified from driving for being unlicensed.

In May, he was suspended for a month for reckless riding in the Grand Prix Stakes.