The Craig Widdison-trained Cash Crisis has returned an elevated TCO2 reading in a pre-race blood swab taken at Sandown.
Cash Crisis was tested before finishing sixth in a 1300m-race on February 6.
Racing Analytical Services Limited reported the blood sample contained a total carbon dioxide in excess of 36 millimoles per litre in plasma, constituting a prohibited substance under Australian Rules of Racing.
A reserve portion tested by the Racing Science Centre also showed a TCO2 reading above the threshold.
Stewards told Widdison of the findings on Monday and their investigations are ongoing.