Northern Ireland ace Shiels was taken off midway through the first half in Rangers' 5-1 victory over East Stirlingshire on Saturday and Wallace also picked up an injury but played the 90 minutes.
Both now look to be struggling for the trip to Westfield as the Light Blues look for revenge following last season's shock 3-2 League Cup exit to the Bairns.
Ally McCoist, speaking at his pre-match press conference at Murray Park, said: “Dean is struggling with a thigh knock he got on Saturday, there will be a doubt also about Lee Wallace as he took a kick.
“Lee’s hopeful he will make it but that will be touch and go as well.
“But we know all about Falkirk, we didn’t do well against them at all last year in the cup tie.
“I think they are one of the favourites or one of the better sides in the division they are in.
“They have a good young manager that’s played at the top level and is certainly very thoughtful about his football.
“So it is a great game for us again, we have a couple of cup ties coming up and the whole thing is still exciting for us at the moment and fresh.
“It’s great and I think all the cup ties this season will have as much, if not more, significance this season than in many years."
He said: “You know we’re now in a position where every game is important to the club.
“It would be totally wrong not to treat the Ramsdens Cup with anything other than total focus and a desire to win it.
“That’s the case, I don’t think we have ever won the Ramsdens Cup so it would be fantastic for the club to go and do that.
“But equally there will be tough games along the way, starting with Falkirk.
“I know big Elvis well, he’s a good lad and I played with him and against him.
“He probably wont be happy with the league start they have had but at the same time they’ll certainly improve because I don’t have any doubt they are one of the better teams in the league.
“He’ll have them organised and raring to go again."