Ross Lyon says Fremantle can't rely on dominant duo Nat Fyfe and Aaron Sandilands, and has challenged his midfield to stand up for a "significant challenge" against Adelaide on Sunday.

The Dockers have confirmed veteran ruckman Sandilands will miss a second match due to concussion, joining suspended skipper Fyfe on the sidelines.

Recruit Brandon Matera, who starred in the midfield and booted three goals for Peel last Saturday, has been recalled to replace Fyfe.

Key defender Alex Pearce (ankle) and Lachie Neale (calf) are expected to be fit.

The Dockers last played without either of Fyfe and Sandilands in round 14 last year in Geelong and threatened a major upset, only going down by two points.

Lyon was in a jovial mood speaking at Optus Stadium on Friday, and had some fun when a reporter quizzed him about facing the Crows with no Fyfe and no Sandilands.

"No hope? I've heard that one before," Lyon joked.

"It's a significant challenge and Adelaide aren't without their challenges (through injury).

"We can't be a midfield group that survives and relies on Sandilands and Fyfe, because if that's the case we're in a lot of trouble.

"Our midfield coaches and our midfield understand they'd like to be more competitive than they were against a dominant ruckman (in Collingwood's Brodie Grundy), and (Sam) Jacobs is a dominant ruckman.

"So the same challenge lies in front of us and we'd like to think we adapt in a strong manner.

 "In the past, we've had strong personnel out and been able to get out and find a way.

"We want to fight tooth and nail and scrap." 

The Dockers are likely to name two ruckmen, but Scott Jones' spot could depend on the weather with rain forecast for Sunday.

Lyon said Sandilands failed his cognitive state test by "a wide margin" and the Dockers were being extra cautious with the 35-year-old.

"There's opportunities to re-test tomorrow, and closer, but we think that's just a bit risky," Lyon said.