Brisbane jockey Ric McMahon has been stood down indefinitely because of an irregularity in a drug test.

Racing Queensland chief steward Allan Reardon said stewards and integrity officers were now waiting for the results of a B sample test and would not comment on reports the drug was methamphetamine, commonly known as ice.

"In fairness to everyone that is all I can say at this time" Reardon said.

McMahon was replaced on his rides at Gatton on Friday and Doomben on Saturday.

Matthew McGuren has picked up the ride on Kaypers in Saturday's feature race, the Listed Tattersall's Mile at Doomben.