In a major blow to the Western Force's Super 14 credentials, Drew Mitchell admits his chances of representing Australia at the 2011 World Cup will be boosted by moving to the east coast.

Mitchell will announce on Friday he's leaving the Force at the end of the season to link up with the NSW Waratahs, where he will replace the Cardiff-bound Sam Norton-Knight at fullback.

And in a parting shot at the Force, Mitchell hinted his decision to leave the Perth-based club was not based around money but rather enhancing his chances of national selection.

Mitchell, a talented winger/fullback who has 29 Test caps to his name, played a starring role at the 2007 World Cup in France.

The 25-year-old scored seven tries in four games but is eager to play a greater role when New Zealand hosts the game's showpiece in 2011.

"A number of things come into (the decision to leave)," Mitchell told Perth radio station 96FM on Thursday.

"It's not at all (based around money).

"In two years' time we've got a World Cup coming up.

"The disappointment of the last World Cup still rings true with everyone involved so I guess putting yourself in the best position to be selected in that obviously comes into it."

Mitchell's comments will be another shot to the heart for the Force, who are frantically trying to convince the out-of-contract Richard Brown, scrumhalf Josh Valentine and teenage prodigy James O'Connor to remain with the club.

Star flyhalf Matt Giteau (Brumbies) and former Wallaby Scott Staniforth (Japan) have already confirmed they will fly the coop at the end of the season, leaving the Force light on firepower in the backline.

Giteau said Mitchell would feel a weight come off his shoulders once he made his intentions public.

"I'm sure once any player decides where they want to go, or where they want to spend their future, your mind's a lot clearer and you can focus on rugby," Giteau said.

Mitchell said he wanted to inform his teammates first before making his decision known to the public.

"Tomorrow we've got a game (against the Lions at Subiaco Oval) so I guess if this can lessen the distraction for the team's preparation leading into the game then that's the best case for everyone," he said.

"We will make a release tomorrow.

"Obviously no one's going to speak before the game and I'll face the storm after the game."

Meanwhile, Brown has been ruled out of the must-win match against the Lions with an ankle injury.

Tamaiti Horua will fill the void, with Richard Stanford earning a call-up to the bench as cover.

And the Force could also be without skipper Nathan Sharpe, who failed to train on Thursday after succumbing to a stomach bug.

The Lions have notched just three wins this season but Giteau said the Force would enter the game with a cautious approach.

"They may not have won too many games but they've been pretty close and scored a lot of tries," Giteau said.

"As a side they can attack from everywhere."

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