Apprentice James Innes Jr has been rewarded with a Group Three opportunity for his time and effort with Nivison Stakes favourite Diddums.

Indentured to Gerald Ryan at Rosehill, Innes has won on the mare twice and been placed three times from five rides.

But he missed out when she claimed her biggest win so far in the Group Three P J Bell stakes in April when she was ridden by the Hong Kong-based Sam Clipperton.

"Sammy was coming out and James stood aside for him," Ryan said.

"They are good friends and he understood.

"The owners Torryburn Stud thought they would repay him with the ride in the Nivison.

"James rides her trackwork and knows her well so it's a great opportunity for him.

Ryan, who also saddles Samantha in the 1200m-race for mares, says he is a little surprised Diddums has come up favourite given the quality of the opposition which includes the well-performed Ron Quinton-trained pair Daysee Doom and Dixie Blossoms.

"I was a little surprised even though Diddums is going really well," he said.

"But if the rain stays then I think Samantha has good wet track form and could be right there."

Diddums was at $3.80 on Friday with the track in the soft range while Samantha was an $18 chance with Ryan's former apprentice Josh Adams to ride.

Samantha won the Listed Fireball Stakes (1100m) in March on a heavy track before running second in the Group Three Birthday Card and finishing out of the placings in the P J Bell.

Diddums will have new shoes with the cushion plates to come off and regular race plates on, a change Ryan says is weather-related.

"In my experience, horses don't perform as well in the cushion plates on wet tracks as they do on dry," he said.

"So I rang the stewards and asked if we could change and they agreed."

Stablemate Albumin is among the fancied runners in the Listed Brian Crowley Stakes (1200m) but Ryan admits he is uncertain about his chances if the track deteriorates.

"He has to be a question mark," he said.

"He has only had one start on the wet as a two-year-old and didn't really handle it.

"He is a stiff-legged horse and they tend not to go well on heavy so it depends how wet the track is."