Left-back Wallace, 29, has not played since picking up a hamstring injury in the 1-0 win over Inverness Caledonian Thistle on 24 December.
Striker Garner, 28, sustained a dislocated shoulder in the 2-1 defeat by Celtic on 31 December.
Meanwhile, boss Mark Warburton has hinted at one more January signing.
Warburton, who revealed forward Joe Dodoo had "tweaked a groin in training", has already brought in midfielders Emerson Hyndman and Jon Toral on loan from Bournemouth and Arsenal, respectively.
"If we can get the right one then we will move but the right ones are few and far between," Warburton told his club website ahead of Saturday's Scottish Cup meeting with Well at Ibrox.
"Whether anyone goes out depends. You never ever know in the market but right now no.
"The scan [on Garner's shoulder] revealed the damage to be not too serious but obviously he has dislocated his shoulder so there is a period of rehabilitation. Joe will hopefully be back training within a week or so and then back with us within two or three weeks.
"There is no surgery required right now. There is always a risk involved in it but the specialist and our medical team are happy with that risk and we'll see how he goes.
"Lee is fit, he will be back training [on Tuesday], he trained with the rest of the squad on Saturday and will be available for selection, touch wood, for the weekend so he will train with us all week.
"Lee is a good athlete and we're looking forward to welcoming him back."
Rangers expect to have captain Lee Wallace back to face Motherwell on Saturday, while striker Joe Garner could return in early February.