The high-profile inquiry into alleged race day treatments of horses in Victoria is set to get underway without its biggest names.

The hearing, which begins on Monday in the County Court in Melbourne, is expected to take two weeks but already multiple Group One-winning trainer Robert Smerdon has said he will not attend as have his former employees Greg and Denise Nelligan.

Smerdon handed in his trainer's licence and unsuccessfully challenged the Racing Appeals and Disciplinary Board's jurisdiction to hear the case against him.

The RAD Board said as he was licensed at the time of the alleged offences dating back seven years, he was bound by the rules of racing.

At a directions hearing, the Nelligans tried to plead "no contest" which was rejected.

They said they would not take part in the inquiry and both were warned off meaning they cannot set foot on any racecourse or facility relating to racehorses.

Greg Nelligan, Smerdon's former stablehand and float driver, is the person believed to be at the centre of the administration of bicarbonate to horses on race day.

Many text messages retrieved from Nellligan's phone have been published in Melbourne's Herald Sun and refer to "top-ups" being given to horses.

Bicarbonate is used to help prevent the build-up of lactic acid but cannot be used within one clear day of a horse racing.

The investigation was sparked after the Smerdon-trained Lovani was withdrawn from a race at Flemington on October 7 last year when stewards suspected a race day treatment.

Smerdon and the Nelligans are among eight people charged under an Australian racing rule dealing with dishonest, corrupt or fraudulent, improper or dishonourable action.

Stewards says that on 115 occasions between 2010 and 2017, Smerdon was a party to the administration of alkalinising agents and/or medications to a horse or horses on a race day.

Among the others charged are trainers Liam Birchley, Stuart Webb and Tony Vasil who, like Smerdon, have all at some time operated under the banner of management company, Aquanita Racing.