Jim Cassidy will get the chance to celebrate a unique milestone at Randwick on Saturday following Chris Waller's decision to start Hawkspur in the George Main Stakes.

Waller has confirmed the Queensland Derby winner will take his place in the 1600 metre feature, rather than the Hill Stakes (2000m).

If Cassidy triumphs he will join only two other Australasian riders to have ridden 100 or more Group One winners.

The Australian record of 119 is held by George Moore with Roy Higgins (104) the other member of the elite club.

Cassidy brought up his 99th career Group One at Rosehill last weekend when he combined with Waller to claim the Golden Rose aboard Zoustar.

Early markets suggest the trainer and jockey will again be celebrating with Hawkspur, a $2.70 favourite.

TAB spokesman Glenn Munsie expects the Cassidy factor to have a significant bearing on totalisator betting given a predicted weight of sentimental support.

"The fact he's going to be on a favourite to ride his 100th winner, Hawkspur is going to be short the tote," Munsie said.

Hawkspur was a dominant last-start winner of the Chelmsford Stakes, run over the same course and distance of the George Main.

However, Munsie has questioned whether there should be such a price discrepancy between the four-year-old and Streama ($7.50) who beat him home at her only start this campaign in the Warwick Stakes.

"Is he entitled to be so much shorter than a horse like Streama who hasn't had that extra run and couldn't possibly get as bad a run as she did at Warwick Farm where she had to cart the field up to Rain Affair?" Munsie said.

"The thing about this race is there doesn't look to be any great speed."

"It's more a battle of tactics than anything else."

The Guy Walter-trained Streama looks the likely leader and will be striving for her first Group One success as a mare.

Her two wins at the top level came in her three-year-old season.

She is one of two mares in the George Main along with Hawkspur's stablemate Royal Descent.

Dissident will be striving to become the first three-year-old to win since Viscount in 2001 after trainer Peter Moody confirmed he will back-up from his courageous second in the Golden Rose.

Tim Clark has been given permission to ride the colt 0.5kg over his 50.5kg.