A stewards' inquiry into the poor performance of racehorse More Joyous which sparked a public spat between John Singleton and Gai Waterhouse will resume on Monday.

The horse's high profile owner Singleton, its trainer Waterhouse and her bookmaker son Tom are all due to front the inquiry in Sydney after the highly fancied mare ran second last in the All Aged Stakes at Randwick on April 27.

Singleton publicly sacked Waterhouse after the race, having accused Tom of telling people More Joyous could not win.

After learning of Singleton's comments, Racing NSW stewards called him to a 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.

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.