Geelong coach Mark Thompson has described Saturday night's AFL clash with Sydney as the club's biggest game of the season, but says the Cats will go into it without injured big men Brad Ottens and Tom Harley.

With the teams from second to fifth positions on the ladder, including the third-placed Cats, all on 36 premiership points, and the sixth-placed Swans on 32, Thompson said the SCG encounter would effectively be an eight-point match.

"This game is huge, if we win it really does set up our season and to be honest its a big challenge up in Sydney," Thompson said.

"But if we do happen to come home with the points it will be season-defining, we're treating it that seriously."

The Cats have won just one of their three previous interstate matches this season.

Thompson said forward Ottens, who has missed the club's past two games with a groin strain, would again be sidelined.

And centre half-back Harley, who missed last week's win over Hawthorn with knee and hamstring problems, was likely to be out for several more matches.

"We're just going to make sure we get Tommy right, we've been mucking around with him all year, putting him in one week and out the next," he said.

"We've just made a strong commitment to him to get his body right and playing when he is right."

Ruckman Steven King, who has struggled with shoulder problems this season, could also be in doubt after he failed to train today.

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