Eagles ruck duo Nic Naitanui and Scott Lycett have dominated rival AFL teams this season, but they have been up against mostly pinch-hitting ruckmen.

That will all change on Sunday when they line up against 211cm Dockers ruckman Aaron Sandilands.

The 35-year-old has been in hot form this season and tallied 53 hit-outs in last week's 54-point win over the Bulldogs.

Gaff said the team's midfielders are aware that Naitanui and Lycett won't be as dominant this week.

"I think it's almost 50-50," Gaff said of the upcoming ruck battle.

"You can't go into a game against Sandilands thinking you're going to win 100 per cent of the taps.

"It's that fine line between thinking of your own plans, but also trying to combat them.

"We've got two quality ruckmen with Scotty and Nic. If they can give us first hands, it's up to us little guys to get the job done."

West Coast have won the past five derbies - all by comfortable margins.

But Fremantle have emerged strongly this season, winning three of their first five games.

West Coast are sitting pretty in top spot with a 4-1 record, but Gaff acknowledged they were a bit off the boil in last week's 10-point win over Carlton.

Gaff said Fremantle's midfield of Nat Fyfe, Lachie Neale and David Mundy would be hard to stop on Sunday.

"They're a quality midfield. They're well renowned around the AFL as being one of the better midfields in the comps," Gaff said.

"We know the combination between Sandilands and Fyfe is probably one of the more prominent ones in the AFL, so we're going to spend a lot of time on him.

"We know the game is won and lost in the middle.

"But we've won the last few derbies in a row, so it gives us confidence that we can do the same."

West Coast are hopeful Lewis Jetta (soreness) will be fit to return this week.

Fremantle will be without forward Matt Taberner (foot).

Australian Associated Press