Jamie Richards' record of six training wins in a day at Ellerslie is in jeopardy after one of his Boxing Day winners returned an irregularity in a post-race test.
But the champion trainer's licence is not believed to be in danger as racing investigators suspect a case of cross-contamination.
Richards trained an Ellerslie record six winners at the Boxing Day meeting but one of them, Vamos Bebe, has returned a post-race urine sample irregularity, which the Herald understands is to morphine, after her win in the Listed Hallmark Stud.
The irregularity, which is not officially classed as a positive swab until after the B-sample is tested and an investigation completed, is a double blow for the owners of Vamos Bebe as she is now almost certain to lose the black-type win.
Disqualification of a horse is almost always the outcome after proven drug irregularities even when no foul play is suspected.
That, and a charge of presenting a horse to the races with a prohibited substance in its system, now looks the most likely outcome of the Racing Integrity Unit's investigation.
Sources close to the case have told the Herald the RIU does not believe Richards or any of his staff have been involved in any wrongdoing and the most likely source of the irregularity is cross-contamination, whether from a human handler, feed or absorption.
Richards is the New Zealand trainer for thoroughbred powerhouse Te Akau and has an exemplary record with no previous irregularities. The five other horses he trained to win on Boxing Day also had post-race urine samples taken with no irregularities.
News of the irregularity saw the horse racing rumour machine kick into overdrive yesterday but the reality is any charge proven, or that Richards pleads guilty to, would probably result in a mid-grade fine.
That is standard in cases of presenting a horse to race with a banned substance as opposed to the much more serious charge of administering a banned substance.
RIU boss Mike Godber told the Herald his investigators are working with Te Akau and Richards to find out how the irregularity happened.
Te Akau boss David Ellis has emailed all owners with horses trained by Richards to reaffirm the stable's commitment to answers.
"We want to determine the source of the contamination and are working closely with the RIU on this," wrote Ellis. "Our track record is one of integrity and we operate at all times to the highest ethical standards."