NSW Waratahs have lost No.8 Wycliff Palu to a season-ending knee injury and are sweating on the availability of fellow Wallabies forwards Benn Robinson and Tatafu Polota-Nau for their crucial Super 14 rugby clash with the Brumbies on Saturday week.

Scans on Monday confirmed Palu will require knee reconstruction after rupturing his right anterior cruciate ligament in last Saturday's match against the Crusaders in Christchurch.

He will miss Australia's home and Tri-Nations Tests and he may struggle to be fit in time for the traditional end of year tour.

Prop Robinson has a small fracture in his right forearm, while hooker Polota-Nau incurred ligament damage in his right shoulder.

Coach Chris Hickey admitted the Waratahs wouldn't be able to directly replace Palu, who was voted the organisation's Players' Player for the past two years.

Hickey is likely to move Ben Mowen from blindside flanker to No.8 and restore Dave Dennis to the former position.

He stressed no single player would be expected to pick up the slack left by the primary ball-carrying forward.

"The go forward he gives us is second to none, you simply can't bring someone else in and ask for them to do the job of Cliff," Hickey said.

"It's a up to a number of other players to lift five to 10 per cent, which we know they can do and will have to do."

Hickey admitted both Robinson and Polota-Nau would not have played this week if the Waratahs had not had the bye.

"It's going to be a bit of a waiting game with both Robbo and Tatafu," Hickey said.

"They both have fairly significant injuries and if we didn't have the bye this week they definitely wouldn't be available."

Both frontrowers face a battle to be fit for the April 24 ANZ Stadium clash with the Brumbies, who will overtake the third-placed Waratahs if they win their home game against the Hurricanes this Friday.

Youngster Damien Fitzpatrick has been backing up Polota-Nau off the bench and could be in line to start against Brumbies.

However, Polota-Nau is renowned for his resilience and has missed only two Super games in four and a half seasons.

The Waratahs could also have extra depth at hooker with Wallabies rake Adam Freier back from injury and expected to play for his club side this weekend.

If Robinson is ruled out of the Brumbies game, his replacement is likely to be another Test prop, Sekope Kepu.

Hickey received one piece of good fitness news, with five-eighth Daniel Halangahu expected to be fit for the Brumbies match after being diagnosed with a grade one strain of his right medial ligament.

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