Knee soreness will deny Geelong another key player in round three, as ruckman Brad Ottens will miss Sunday's AFL game against Fremantle at Subiaco Oval.

The Cats, already without their bookends Cameron Mooney and Matthew Scarlett through suspension, ruled Ottens out on Friday because of swelling in his right knee.

"He just had a sore knee from last week's game," Geelong football operations manager Neil Balme said.

"We thought he'd be OK, but he hasn't come up, and we think he'll just miss the one."

Ottens was an influential figure in last Monday's comeback win over Hawthorn, as he starred in the ruck in the second half and took a couple of decisive marks in attack which turned the game the Cats' way.

His sore knee is the same one that troubled him last year and kept him out of most of the home-and-away season, although he recovered in time to play in the win over St Kilda in the grand final.

Balme said the shorter recovery time and long flight to Perth would not help Ottens' knee, but the Cats were confident the big man would play Port Adelaide in round four.

"We're pretty confident if he misses this one he'll be right for the next week," he said.

Ottens' absence means Geelong will play their fourth debutant of the season in Dawson Simpson, who will come up against Fremantle giant Aaron Sandilands, one of the best rucks in the competition.

The absences of Ottens, Mooney and Scarlett give Fremantle a great chance to break a seven-game losing streak against the Cats, who they have not beaten since 2005.

The Dockers are second on the ladder and Geelong fourth after both sides won their first two games.

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