Left-back Davidson is nursing a calf strain sustained in last week's 4-1 defeat at Swansea, while Wallace took a blow to his ankle in the same game.
Both men missed Saturday's goalless draw at home to Sheffield United and are rated as doubtful to face Argyle.
Eddie Nolan and Barry Nicholson could be asked to deputise once again while striker Neil Mellor is recovering from a hernia operation and remains sidelined along with a quartet of long-term absentees.
Goalkeeper Wayne Henderson and defenders Liam Chilvers, Michael Hart and Neal Trotman are all continuing their rehabilitation from injury but none are ready to be considered for first-team selection.
Plymouth have been boosted by the return to fitness of on-loan Manchester United central defender Craig Cathcart ahead of the trip.
Northern Ireland Under-21 international Cathcart was ruled out of Saturday's 0-0 draw at Ipswich due to a back injury, which forced him off in the second half of last Tuesday's 2-0 home defeat by Bristol City.
His replacement on both occasions Portman Road was Hungarian international Krisztian Timar, last season's player of the year.
Boss Paul Sturrock also recalled central midfielder Simon Walton to his starting XI at the weekend as well as fit-again Blackburn loanee forward Paul Gallagher.
Sporting Life.