Williams is battling to board the plane to Australia

Williams, a key figure in the victorious Tri-Nations campaign, is struggling with a fractured foot.

And captain Justin Marshall told BBC Sport that Williams was still a doubt and his absence would be a "massive blow" to his country's Cup ambitions.

"Ali has been struggling for a while now with a bad foot injury," said Marshall.

"And the management will make a decision on Monday.

"As to his chances of making it, I don't know. We've not been told anything else at the moment."

The team fly to Australia for the tournament on Wednesday.

"Should we board the plane without Ali that would be a real shame," added Marshall.

"He has been a really important part of the side to date. He was integral to us winning the Tri-Nations and has been performing really well all the time."

Despite Williams' potential absence, Marshall insisted there were still a host of candidates capable of taking his place.

He added: "The one positive we have here is that Brad Thorne and Norm Maxwell have been in stunning form. Hopefully that will at least make some amends should the need arise."