FREMANTLE big man Rory Lobb is set to miss at least the first six rounds of the season despite avoiding surgery on his injured right knee.

Lobb's knee twisted at a dangerous angle while being tackled during the club's AAMI Community Series loss to West Coast on Sunday.

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Scans revealed Lobb had suffered major damage in the incident, but the good news is his anterior cruciate ligament wasn't torn.

Instead, Lobb suffered a strain to the ACL, as well as significant damage to the posterolateral corner in his knee.

Fremantle were concerned about the potential for meniscus damage as well, but the medical opinion is Lobb won't require surgery.

The 28-year-old, who has rotated between ruck and forward-line duties for Fremantle, will spend the next six weeks in a brace before being reassessed.

With Fremantle's season-opener just 11 days away, Lobb appears set to miss at least the first six rounds given he'll need to build up his fitness again once he is out of the brace.

Veteran forward Michael Walters will also miss the start of the season due a hamstring injury that will sideline him for three to four weeks.

The news is even worse for Bailey Banfield (syndesmosis) and Mitch Crowden (calf), who will miss at least the next five to six weeks.

The loss of Lobb is the biggest blow to Fremantle given his importance to their structure.

With Lobb now out of action and No.1 ruckman Sean Darcy (knee) no certainty to face the Demons in round one, Fremantle looks set to hand a debut to untried ruckman Lloyd Meek.

Rookie forward Josh Treacy is also set to be handed an AFL debut to help fill the void left by Lobb up forward.

Dockers coach Justin Longmuir says he will also consider swinging one of his key defenders into attack.

Brennan Cox started his AFL career in the forward line, but Longmuir will be reluctant to take the 22-year-old out of defence given his stunning form there last year.