Chris Waller has flagged the possibility of scratching Moriarty from the Doncaster Mile if the Randwick track is downgraded to a heavy rating.

The surface was rated a soft six on Thursday but showers have been forecast for Sydney on Good Friday and Saturday.

Waller confirmed he would reconsider a start for Moriarty if the track got significantly worse.

"Obviously Moriarty is a doubtful runner if the track is heavy. He has had eight goes on a soft or heavy track for one placing," Waller said.

"There would be some concern on him should we get a heavy track."

Waller has two-time defending champion Sacred Falls and Royal Descent in the Doncaster Mile field, while three-year-old Kermadec is second emergency and needs two scratchings to gain a start.

If Moriarty is withdrawn, first reserve Sweynesse will join Godolphin stablemate It's Somewhat in the Group One line-up.