Former Sunderland and Hearts goalkeeper Gordon is without a club and has been training with the Light Blues.
Boss Ally McCoist is keen to strengthen the position after confirming Neil Alexander is unlikely to remain with the Third Division champions next season.
Asked for his thoughts on Gordon, Foster said: “He’s an international goalkeeper.
“Everyone agrees that, when he’s fit and playing, he would be in the Scotland set-up.
“Signing someone like that would be massive.”
Foster agreed a two-year deal with Rangers following his release from Bristol City and will complete his move on September 1 when the club’s transfer embargo is lifted.
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