Magic Millions-winning trainer Darryl Hansen has been found guilty of a presenting a horse to race with a TCO2 level above the allowable level.

The Sunshine Coast-based Hansen has until Friday to make submissions to stewards regarding penalty.

An inquiry at Racing Queensland's headquarters on Wednesday heard two samples were taken from Hansen's horse How Can I Help which raced at Ipswich on August 14, finishing fifth.

Chief steward Allan Reardon said the first sample showed a TCO2 level of 37.4 millimoles per litre in plasma which was above the threshold of 36 but the second was 36.5, within the legal range allowing for a 1.0 measure of uncertainty.

The inquiry heard a stable employee might have mistakenly administered a substance containing bicarbonate to the horse's feed.

Hansen had one of his best seasons in 2014-15 with Le Chef's Magic Millions 2YO Classic win earning him the prestigious Wayne Wilson Medal for outstanding performance.