The Saints proved last week they could win without their inspirational skipper, holding Collingwood goalless in the second half to register a gutsy 28-point win at Etihad Stadium.
Harvey said that, while remaining free of serious injury had been a boost for Fremantle, coming up against the Saints without their spearhead might not be.
“It can be an advantage and a disadvantage, depending on how they go inside-[50m]", Harvey said from Fremantle Oval on Wednesday.
“They’re the best defensive side in the competition, St Kilda, we’re looking at how we can possibly break that down a little bit.
“We haven’t seen their side at this stage, but they’ve got some dangerous small forwards and also some midfielders who can kick goals.
“[Brendon] Goddard’s been playing there lately, so it depends how they want to have their structure.”
With Antoni Grover (knee) the only regular player missing through a major injury, Fremantle has maintained stability at the selection table using a total of just 24 players in its first three games.
Injury-hit Adelaide has already used 29.
After beating Geelong minus some of its stars, and the Crows in round one, Harvey said Fremantle had been coming up against sides at the right time.
“Some of these other sides have had significant injuries in the first few weeks,” the coach said.
“At the moment we’re probably meeting teams at the right time and we’re taking advantage of that.
“A lot of the sides that finish up in the top four or six, they will have stability in their selection.”
Fremantle will be without Nick Suban (ankle) this week, while Chris Tarrant is set to return after missing the Geelong win.
Harvey said there was likely to be one more change to the side that takes on St Kilda, while he was also considering a second ruckman to support Aaron Sandilands against the experienced Steven King and Michael Gardiner.
“They’ve obviously always got a couple of big ruckman that play for them,” Harvey said, adding that Kepler Bradley was ahead of youngster Zac Clarke.
“We’ll look at that (and) maybe another change, depending on structure and what we need to do being on the road.”
Michael Barlow will be right to take on the Saints, despite copping a heavy knock to the ribs early against Geelong, while Byron Schammer is also being considered.
Harvey said that, after wins over Essendon in round two and North Melbourne in the pre-season, his side would travel to Etihad Stadium fearless.
“Etihad is nearly our second home ground, that’s how we’ve got to look at it,” he said.
