The Western Force are bracing for a double blow ahead of their crucial Super 14 clash against the Sharks on Saturday with Wallabies duo Richard Brown and Cameron Shepherd sidelined.

The key pair are highly unlikely to overcome injuries for the round six match at Subiaco Oval, as is rising winger Nick Cummins.

No.8 Brown will be the most sorely missed, especially after he was expected to make his return from a shoulder injury he sustained while scoring a try against the Brumbies in round three.

Tamaiti Horua was a solid replacement at the back of the scrum in the loss to the Chiefs and 23-23 draw against the Crusaders but the Force pack has struggled without Brown's physicality and work-rate.

The Force are understood to be wary of risking Brown before he's 100 per cent and with a round seven bye looming, are expected to give him an extra fortnight to be fully fit for their April 3 derby with Queensland.

Shepherd, who scored a memorable hat-trick against the Brumbies in round three, is also set to be rested over the next two weeks after injuring the same ankle he broke last year when playing for Australia.

With fellow winger Cummins battling with a hamstring problem, the injuries have opened the door for 2007 World Cup Wallaby Scott Staniforth to return the Force's starting backline.

In some good news, prop Ben Castle appears to have shrugged off a neck-shoulder injury and is set to be named in the side on Thursday.

The Sharks will be without versatile playmaker Ryan Pienaar, a Springbok halfback who plays five-eighth in the Super 14, after he suffered a knee ligament strain in the 25-13 loss to the Reds.

Despite their last-start loss, the third-placed Sharks will be a tough nut to crack for the Force who continue to battle to post wins at home.

Since their inception in 2006, the Perth club has won just eight of their 21 matches at Subiaco Oval.

Fans will be hoping a one-off change of jersey - wearing pink - will reverse their fortunes.

Stars Matt Giteau and Drew Mitchell will also sport pink boots and the field markings will be painted in the same colour.

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