Godolphin's Melbourne Cup contender Cavalryman is in doubt for Tuesday's race with a leg injury.

He was found to have swelling to his near-fore fetlock on Monday afternoon and x-rays have been sent to Sheikh Mohammed's vets overseas.

They will study the x-rays as will Australian vets before a decision is made whether he takes his place in the field.

If he comes out Godolphin will be left with Willing Foe as its lone runner in the Cup it has been trying to win since 1998.

"We've tried for a long time," trainer Saeed Bin Suroor said.

"We've finished second three times."

If Cavalryman is withdrawn, Craig Williams will again be denied the chance to complete the grand slam of Australian racing.

Williams needs only the Melbourne Cup to complete the set and join seven other riders to have won the Melbourne Cup, Caulfield Cup, Cox Plate and Golden Slipper.

In 2011, a suspension cost Williams the winning ride on Dunaden in what he describes as the holy grail of world racing.

In another twist, James McDonald was given the choice to switch from Cavalryman to Willing Foe when British jockey James Doyle was suspended.