Gallacher played for Ally McCoist's side in the opening games of the 2013/14 campaign when new arrival Cammy Bell was ineligible.
And the 6ft 2in 24-year-old impressed many Light Blues supporters with his accomplished performances in those outings.
Despite being involved in the painful League Cup defeat to Forfar at Station Park at the beginning of August, he played in wins over Albion Rovers, Brechin, Stranraer and Airdrie.
But when new signing Bell came into the side as a trialist at the end of August he was loaned out to SPFL League One rivals Airdrie.
The keeper did well and played in eight first team games for the struggling Excelsior Stadium club before returning to Rangers last month.
Diamonds manager Gary Bollan, though, has secured the services of youngster Danny Rogers on loan from Aberdeen since then.
So the former Rangers midfielder is unable to take Gallacher back to the Lanarkshire club until the end of the term.
And he is not allowed to go and play for another club as he is only allowed to play for two clubs during the course of a season under Fifa rules.
With Bell enjoying outstanding form and the vastly-experienced Steve Simonsen acting as back-up, he is not set to be involved in the first-team squad on match days.
But Rangers coach Ian Durrant stressed that Gallacher will get regular competitive football.
Speaking to the official Rangers website, he said: "Scott can only go back to Airdrie, but they've taken someone else in.
"That means he'll be with us and he's under contract here so that's fine. It's a shame for him because we've got so many goalkeepers here.
"Barring injuries to Cammy and Steve, Scott will be playing reserve football."