Nathan McPherson is the latest trainer to be fined after being found guilty of administering a raceday treatment to a horse.

McPherson was hit with an $8000 fine after stewards ruled he had treated Testaguy with an unknown substance by way of injection on the day he was due to race at Mornington on January 28.

Two members of Racing Victoria's Compliance Assurance Team went to the property where McPherson's horses were stabled and saw two men standing with a horse, one of whom appeared to have a needle in his hand.

The men were later identified as McPherson and former jockey Greg Hall who is not a licensed person under the rules of racing.

When Compliance Assurance Team member Mark Stevens inspected Testaguy he said he found what appeared to be a puncture wound on the neck and blood was visible.

When later asked to empty his pockets, McPherson produced two syringes which he said had been used to treat another horse on the day.

Mcpherson pleaded not guilty at Thursday's hearing but stewards accepted the evidence of the Compliance Assurance Team.

Testaguy was not allowed to race.

After recent inquiries, trainers Robert Smerdon, Tony Vasil, Jim Conlan and Ricky Maund have been fined $10,000 for raceday breaches.

West Australian trainer Adam Durrant, who was also fined $10,000 for the same breach, has appealed his penalty.

Stewards, headed by Brett Wright, said they believed an $8000 fine was appropriate for McPherson, who has only been training for just over a year.

The trainer said he had already lost some horses because of the publicity surrounding the incident.

"I've lost some clientele. I've lost eight horses, five left yesterday morning," McPherson told stewards.

McPherson said he would consider an appeal.