Chris Waller's best chance of winning his fifth Doncaster Mile rests with a horse who is not guaranteed a start.

Three-year-old Kermadec is second emergency for the $3 million race and needs two scratchings to make the field.

One of them is likely to come from his own stable with Waller saying the predicted downgrade to a heavy track would rule veteran Moriarty out.

Kermadec is the most highly rated of Waller's Doncaster contenders at $8 ahead of last year's runner-up Royal Descent at $9.50.

Sacred Falls, attempting to become the first horse to win the race three times, is a $21 chance with Moriarty at $71.

The trainer has made the Doncaster his own in recent years with four wins in the past seven runnings and is not convinced the market has it right.

"It's hard to say. One of them has won two (Doncasters), one has run second last year with the same weight and same draw. Kermadec hasn't been to that level yet," Waller said.

"He's been unlucky in two Group Ones so he's the up-and-comer, but there is no use talking about him if he doesn't get a start."

Royal Descent heads into Saturday's race in arguably better form than 12 months ago.

She finished fifth against the mares in the Coolmore Classic in her final lead-up run last year and fourth against the males in the George Ryder Stakes this autumn.

"She all but won the race last year and Nash Rawiller got off her and said she was beaten by a freak performance by Sacred Falls on the day," Waller said.

"History repeats itself and in my opinion she is ready to go again and the run in the George Ryder was very good.

"Third-up is a pretty proven formula with her."

Joao Moreira links with Royal Descent for the first time while fellow Hong Kong-based jockey Zac Purton returns to try to win it again on Sacred Falls who will carry 1.5kg more than last year.

Both horses are drawn wide with Royal Descent in gate 18, the same barrier she jumped from 12 months ago, and Sacred Falls two to her outside.

"It's going to be hard from barrier 20 but as we've seen recently the fence has always been a concern at Randwick so late in the day maybe barrier draws are not as significant," Waller said.

Doncaster favourite Hallowed Crown ($5) has drawn one from the outside. He will be ridden by Tommy Berry who rode Sacred Falls to the first of his Doncaster wins in 2013.

Hallowed Crown has a perfect record of three wins from three starts in the wet.