Former Wallabies halfback Brett Sheehan will be sidelined for three months after undergoing surgery on his injured knee, ruling him out of the Western Force's two-game rugby tour of Samoa.

Sheehan suffered medial ligament damage to his left knee while playing for Sydney Shute Shield side Warringah in last Wednesday's shock win against the previously-undefeated Eastwood.

Force coach Richard Graham said he expected Sheehan to be ready for the start of the pre-season on November 1, leaving reserve scrumhalf James Stannard to take the lead role at No.9 in games against Samoa on August 21 and 28.

With the Force's other reserve scrumhalf Justin Turner still recovering from a serious knee injury and fellow No.9 Mark Swanepoel having left to explore other options in New Zealand, Graham said he was scouring the country for other alternatives to take on the tour.

"We've got Stannard who can play there and, at the moment, I'm looking to find the best No.9 in the country that's not contracted (to use as a back-up)," Graham said on Tuesday.

"We let Swanny (Mark Swanepoel) go to play some ITM Cup (in NZ) through this period of time to get some good quality rugby so I'll just continue to look throughout the country (for other options)."

Graham said the matches against Samoa would be a stern test after watching the rugby minnows inflict a shock 32-23 defeat on the Wallabies last month.

"It's going to be exactly what we need and we hope to provide them with exactly what they need," Graham said.

"It's their last two games going into the World Cup.

"People would be very familiar with their performance against the Wallabies. They are a physical side. For us, that's one of the great challenges."

Graham has invited Wests flanker Angus Cottrell and Eastwood centre Tim Bennetts on the tour, with the pair looking to earn a permanent contract with the Force.

Nedlands flanker Will Brock, who was part of the inaugural Western Force academy before plying his trade overseas and in the Shute Shield, will also join the touring party.

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