Little and Templeton have not played in the last month, while Wallace picked up an injury in Sunday's Ramsdens Cup final defeat by Raith Rovers.
"Lee has a hip flexor problem at the top of his thigh and he's struggling a little bit," McCoist told the club's website.
"We'll give him every chance, but I'd have to say there will have to be a dramatic improvement for him to be involved at the weekend.
"I wouldn't think Andy and David will make it though; there would have to be an unbelievable improvement in them.
"We've been a little bit unlucky with injuries at a really important time of the season, but we have to prepare the team as best we can."
On a more positive note, midfielder Nicky Law and strikers Jon Daly and Nicky Clark are all expected to be involved at Ibrox as the Light Blues chase their 52nd appearance in the final of the national showpiece.