The 28-year-old has been ruled out of the Saints' two AFL practice matches - the first of which is against Melbourne next week Friday - after injuring his knee last week.
St Kilda are already missing star Max King, who underwent a shoulder reconstruction late last year and isn't expected back until round five, while Jack Hayes and untried key forward Matt Allison are both sidelined with foot injuries.
Club great Robert Harvey, who has rejoined St Kilda as an assistant under returning coach Ross Lyons, was confident Membrey would be available to face Fremantle in round one at Marvel Stadium on March 19.
"He had minor surgery on his knee yesterday," Harvey said on Friday. "The reports are all good so we are expecting him to be all good for round one.
"He's had a full summer, he's barely missed a session, so we're really happy where he's at - it is a minor setback, so we're totally expecting him to be right for round one."
St Kilda added Anthony Caminiti to their rookie list last week and while Harvey had been impressed by the 19-year-old, he thought it was unlikely the young key forward would be in the selection mix for the opening round.
"It's a big stretch because he's coming from a long way back," Harvey said.
"What I will say is that's he attacking things so well; he's got great attributes, he's athletic, he's good size at 198 (cm).
"We're excited but we won't get too ahead of ourselves for round one ... we're realistic about the developments needed for a guy like him."
Despite the coaching turnover and injuries Harvey expected the Saints to have no excuses come round one, when they will look to implement a new Lyons-led playing style.
"Ross still drives very high standards and we're really clear with what we need to do," Harvey said.
"We're not here to make up numbers so we want to start well.
"As much as there's a lot of talk about injuries we'll have a good side in for round one.
"We're excited and we want to hit the ground running."
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