What began as a routine stewards' inquiry into the poor performance of racehorse More Joyous will continue amid unprecedented publicity on Monday.

High profile owner John Singleton, even higher profile trainer Gai Waterhouse and her bookmaker son Tom Waterhouse are the lead characters due to appear at the inquiry sparked by Singleton's comments after the highly fancied More Joyous ran second last in the All Aged Stakes at Randwick on April 27.

Singleton publicly sacked Waterhouse after the All Aged Stakes having accused Tom of telling people More Joyous could not win.

"Tom has been saying she has got problems and I don't know about them," Singleton told the Seven Network after the race.

"It's too much. It's a conflict of interest."

After learning of Singleton's comments, Racing NSW stewards called him to the raceday inquiry where he declined to name his sources but reiterated his belief there was a problem with More Joyous he should have been told about.

His sources have since outed themselves.

Former jockey Allan Robinson, ex footballer Andrew Johns and punter Eddie Hayson say they are the people involved but say they will not appear at the inquiry.

Robinson, who retired three years ago after suffering serious head injuries in a fall, has given a statement as has Johns but racing officials want to be able to cross examine them if necessary and will try to compel them to attend.

At the inquiry it emerged More Joyous had received an antibiotic on the Thursday before the race after heat was detected in her neck.

Reminded of a trainer's obligation to tell stewards if there was any issue that could affect the performance of a horse in a race, Waterhouse replied: "There was no issue".

More Joyous was examined by stable vet Leanne Begg and Singleton's vet John Peatfield who passed her fit to run but was not examined by Racing NSW vets until after the race.

The following day, Tom Waterhouse appeared on various media outlets to say he had backed More Joyous, and All Too Hard's win was a $300,000 worse result for his ledger.

Stewards will also question Gai's husband Robbie Waterhouse and Singleton over a reported altercation between the pair at Randwick after the initial inquiry.