Wodonga tainer Brian Cox was taken to hospital after collapsing soon after the resumption of a Racing Appeals and Disciplinary Board hearing on Wednesday.
Paramedics were called to the Epsom Road headquarters of Racing Victoria to assist Cox, who fell to the floor inside the hearing just moments after asking for a brief adjournment due to not feeling well.
The trainer was back in the witness box on day three of the hearing under cross examination from legal counsel for RV stewards, Jack Rush QC.
He remained in hospital under observation late on Wednesday, but is expected to re-appear at some stage during the hearing which has been slated to run all week.
Cox is answering charges including the alleged administration of a prohibited substance and alleged improper conduct.
He has pleaded guilty to three charges including possession of the banned substance, Nitrotain, and manhandling a steward.
The hearing resumed after Cox was taken to hospital, with his wife Janet and stablehand Amber Comb giving evidence.
The trainer began the day with an apology for comments he had made the previous day about Racing Victoria stewards including chief steward Terry Bailey, who has sat in on every day of the hearing to date.
Comb has been a part-time employee with Cox Racing since 2010 and told the hearing she had never seen Nitrotain used at the stable since its ban two years ago.
The previous day, former stable colleague Anika Basiak, said she had witnessed the banned substance used on two horses last August.
Comb said Basiak and Cox had an "up and down relationship" during her third stint at the stable.
She was also aware Nitrotain had been kept in the stable tea room fridge since the ban came into effect.
Comb said it was a "silly decision" to keep the substance at the stable, but never questioned Cox.
Comb is also an amateur jockey and has ridden racehorse Cochranes Gap in trackwork.
The horse is at the centre of an animal cruelty charge levelled at Cox by stewards.
The stablehand said she wasn't aware of any other staff members expressing concerns Cochranes Gap was being worked despite having a leg wound in the lead-up to a jumpout at Wangaratta on December 8 last year.
Comb said the horse had shown no signs of lameness.
Janet Cox appeared briefly in the witness box and rejected an earlier claim that she was handed an empty Nitrotain tub for disposal after the substance was transferred into another container.
The hearing continues on Thursday.