Wallaby prop Benn Robinson's unlikely bid to be part of the World Cup has fallen flat and he will now undergo knee surgery on Tuesday.

Robinson had planned to try to delay the surgery to repair a ruptured anterior cruciate ligament until after the tournament by way of some kind of miracle, but has finally admitted defeat.

This will be the second World Cup in a row that the 27-year-old will miss, after he was unlucky to be a late omission four years ago.

"Heading in for surgery tomorrow !! Pushed really hard to make it but knee just isn't right !! Very disheartening !!" Robinson announced on Twitter on Monday.

Several Wallabies will need to pass fitness tests on Wednesday before coach Robbie Deans names his World Cup squad on Thursday.

Props James Slipper, Ben Daley, hooker Tatafu Polota-Nau, No.8 Wycliff Palu, wing Drew Mitchell, centre Rob Horne and utility back Berrick Barnes are all in a race against the clock to recover in time to be part of the Australian team at the global showpiece.

Former Wallaby coach Bob Dwyer believes that the best players must be taken even if there are injury concerns surrounding some of them.

"It think we need all our best players if we are going to make a good fist of this," Dwyer told AAP.

"We're not that good that we can play without them so the sooner they get back the better."

Deans admitted that the way some of the fringe players had performed in the Tri-Nations was not making his selection process any easier.

"We've got some tough calls to make. There's going to be some pain," Deans told AAP.

"But I guess the good thing is, we're in that circumstance now."

The coach has also stressed that players who aren't named in the squad mustn't lose hope, as there are always injuries that could open the door again.

"The wheel turns and I've got no doubts there will be opportunities - there will be injuries," he said.

"You don't wish that on anyone but that's the likelihood.

"You just hope that anyone who doesn't make it holds on to that prospect that they could get a call-up and they could end up playing in a key game," he added.

"These opportunities (to play in a World Cup) don't come around very often.

"But in the first instance there will be some disappointed good players."