Fremantle coach Justin Longmuir is optimistic Rory Lobb has avoided an anterior cruciate ligament tear as the Dockers count the cost of their 10-point western derby loss to West Coast.

Lobb's right knee and ankle both twisted at awkward angles when he was tackled by Tom Cole in the first quarter of the 9.13 (67) to 8.9 (57) defeat in front of 20,166 fans at Optus Stadium.

The Dockers big man immediately grabbed at his knee, and he could barely put weight on his right leg when he was eventually helped off the ground.

Lobb was later spotted wearing a knee brace and using crutches.

"We're reasonably confident it's not worst-case scenario," Longmuir said.

"But we need to have it scanned before we put anything to bed.

"It's the worst possible time to get injured. But he was pretty positive. He's holding out hope of dodging a bullet."

Even if he has avoided an ACL tear, any medial ligament damage could rule him out for anywhere between four to 12 weeks.

Lobb's injury comes at an unfortunate time for the Dockers, with No.1 ruckman Sean Darcy only "touch and go" for round one due to a knee injury.

Star forward Michael Walters will miss the start of the season after tearing his right hamstring in the third quarter.

"He's done it before. He said it's low grade," Longmuir said.

Untried big man Lloyd Meek is likely to be given the lead ruck role for the round-one clash with Melbourne at the MCG, while first-year forward Josh Treacy could also debut.

Longmuir will also consider swinging one of his key defenders up forward to fill the void left by Lobb.

West Coast didn't come away unscathed either from Sunday's match.

Zac Langdon was stretchered off in the third quarter after a sickening clash of heads with Nat Fyfe that knocked the Eagles recruit out cold.

Fyfe was able to get up almost straight away, but a clearly groggy Landgon couldn't even support the weight of his head when he tried to sit up.

Eagles skipper Luke Shuey injured his ankle in the third quarter, while defender Brad Sheppard received a knock to the head from Darcy Tucker.

Shuey didn't return, but it was more a management decision rather than concern over the injury.

Sheppard returned, before copping a knee to the head from Bailey Banfield in the final quarter.

Banfield injured his right ankle in the incident, while Sheppard was left with blood streaming from his head.

"I think Zac's OK, he's walking around, he's talking so that's a positive," Eagles coach Adam Simpson said.

"And I think Shep's got some stitches the poor bugger. He broke his nose two weeks ago and got some stitches in his forehead today."

Eagles defender Jeremy McGovern faces a nervous wait after dishing out a high bump on Lachie Schultz.

Eagles forward Liam Ryan booted three goals and set up numerous other attacks in a dazzling display, while Fyfe starred for Fremantle with 27 disposals, 10 clearances and a goal.