The champion Hong Kong jockey limped back to the jockeys’ room after the fall in the fourth race at Flemington on Tuesday and was stood down from his remaining rides.
The lightweight Allen was the only rider in the jockeys’ room able to ride the Willie Mullins-trained stayer at 52kg.
Thomas Hobson, one of three runners for Mullins, is at $21 with 2015 Cup runner-up Max Dynamite at $16 and Wicklow Brave a $51 chance.
Moreira hit the ground when the Chris Waller-trained Regal Monarch came down near the 300m of the Ronald McDonald Plate (280m).
Regal Monarch has been taken to the Werribee veterinary centre with a suspected shoulder injury.
Credit: AAP