A horse trained by Peter Gelagotis has returned a positive sample to a prohibited substance on race day, with Racing Victoria stewards continuing their investigations.

RV stewards have told Gelagotis a pre-race blood sample taken from Strong Influence before the gelding ran at Sandown on June 26 was shown to contain a total carbon dioxide (TCO2) at a concentration in excess of 36.0 millimoles per litre in plasma.

In accordance with the rules of racing, a reading above 36 ml/L in plasma is therefore a prohibited substance.

Four-year-old Strong Influence finished third in the 1300m benchmark-70 race as the $3.20 favourite.