Fremantle ruckman Aaron Sandilands is likely to spend most of Friday night's AFL semi-final showdown with Geelong on the ground in a bid to prevent his injured knee from seizing up.

Dockers coach Mark Harvey has declared Sandilands a certain starter against the Cats, although doubts still remain about whether the 211cm giant will be able to fulfil his full rucking role.

The dual All-Australian spent most of last week's win over Hawthorn in the forward line but Harvey hoped Sandilands would be able to spend more time in the ruck against the Cats.

"If you have a look at a lot of Aaron's ruck duels, no matter where they are, he doesn't jump a hell of a lot," Harvey said on Wednesday.

"For how long and how many times (he can contest the ruck), we'll wait and see.

"Once again we have to see how quickly his injury can come up as to what he can do.

"Every minute, every hour that goes by, the response has been really positive. That's all we can judge it on at the moment.

"Naturally, we'd probably like to see in the next 48 hours what he can do so at some stage we'll have a look at him over in Melbourne."

When asked whether Sandilands would need to rest up forward instead of spend time on the bench in order to prevent his knee from seizing up, Harvey said: "We'll probably keep him on the ground a bit longer, which should be a headache for Geelong."

The Dockers will fly out to Melbourne on Wednesday night and train at the MCG on Thursday.

Fremantle will take over a squad of 25, with Des Headland, Paul Hasleby, Kepler Bradley and Rhys Palmer all in line to travel with the team after being overlooked for selection last week.

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