Marshall is one of the league's most accurate goalkickers, with the 24-year-old following up his 45.15 last season with 34.15 so far this campaign.
But he had some forgettable moments in the 48-point qualifying final loss to Brisbane at the Gabba last week, with two of his close-range set shots not even registering a score.
One of them - from 25m out on a slight angle - skewed off the inside of his right boot so badly that it didn't even come close to scoring.
Marshall missed the final round of the home-and-away season with a hip injury, and Port assistant coach Nathan Bassett revealed the 198cm forward was no certainty to face GWS this week.
"It wasn't a great night for us. We missed some easy shots," Bassett told reporters on Monday.
"Todd's got a few extenuating circumstances around his kicking.
"He's had some hip issues. We're waiting on a few scans today, and he's one of them.
"We'll find out more (on Tuesday) morning. I'd imagine he'd be in some doubt."
Port are also sweating on the fitness of defenders Dylan Williams (hamstring) and Trent McKenzie (ankle).
But in better news, Charlie Dixon is on track to return from a fractured foot that has sidelined the spearhead since round 20.
"Charlie's run four times. He will certainly push to train and he'll want to play this week," Bassett said.
"Charlie's a great competitor and he holds other people to account as well in the forward line and across the team.
"It's always nice to have his presence out there."
Retiring skipper Tom Jonas, who injured his calf during the last minute of training last Thursday, hasn't given up hope of returning this season.
"I don't think the scan was too bad on his calf," Bassett said.
"He hasn't gone into full retirement mode just yet. He'll certainly keep going and attempt to be available."
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