Australian trainer Danny O'Brien is the latest trainer to find himself in hot water, with his galloper Coin Collector returning a blood sample which contained a prohibited substance.

Late on Wednesday afternoon, Racing Victoria stewards announced that they had received a report from Racing Analytical Services Limited (RASL) that showed a blood sample containing Phenylbutazone, which is a non-steroidal anti-inflammatory drug.

The report goes back to a blood sample taken prior to Coin Collector competing at Moonee Valley on All Star Mile Day back on March 13 this year.

The drug is a prohibited substance when found in a sample taken on race day, in line with the Australian Rules of Racing.

Racing Victoria stewards had informed the Melbourne Cup-winning trainer back on April 27 about that irregularity, with the findings only being made public at 4:30pm on May 26.

Stewards have announced that they will be continuing the investigation.

It remains to be seen whether Coin Collector will be disqualified from his third-placed finish at The Valley and his fourth-placed finish at his subsequent start at Sale.