John Singleton has delivered a withering character assessment

John Singleton has delivered a withering character assessment of his long-time friend Andrew Johns over his role in the More Joyous affair, describing him as ''weak''.

The acrimony between the main players in the affair deepened on Tuesday, after an already dramatic hearing at the Racing NSW inquiry on Monday. The rugby league legend missed Monday's hearing but has now agreed to front up when the hearing resumes.

''At this stage I think that Andrew owes me an apology: he needs to front up, needs to man up,'' Mr Singleton said in an interview with Channel Seven. ''I've always trusted Andrew, I've known him since he was 14 years old. But geez, how can you be so strong on the field and so weak off it?''

That interview was recorded before news broke on Tuesday that Johns had agreed to appear before the inquiry.

His evidence is seen as crucial to getting to the bottom of whether bookmaker Tom Waterhouse had talked down the health and form of More Joyous - a horse trained by his mother Gai and owned by Mr Singleton - before it ran second last in the All Aged Stakes on April 27.

Mr Singleton spoke to former jockey Allan Robinson and Johns before the race, who told him that they had learned the horse had health problems.

At Monday's inquiry Mr Singleton implied that Johns had recanted his version of a conversation with Tom Waterhouse days after that race.

Mr Singleton said Johns looked dishevelled and was fearful of being sacked by Channel Nine when he admitted his account of a conversation with Tom Waterhouse may have been ''embellished''.

Mr Singleton said his respect for Gai Waterhouse - More Joyous's trainer - had only grown after her fiery showing at Monday's inquiry, despite her accusing Mr Singleton of being drunk, volatile, using foul language and making false accusations about her and her family.