The Toulouse lock, who was sidelined for most of this year’s Six Nations with a back complaint, was included in Gregor Townsend’s initial squad but has had to pull out with a hip injury.
The SRU has confirmed that Gray will not be replaced in the squad.
Gray went under the knife last year to fix a niggling back injury that kept him out of Scotland’s Summer Tour. The surgery and subsequent recovery time meant he missed the Autumn Tests and wasn’t fit enough for Scotland’s Six Nations opener against Wales.
He returned to the squad for the penultimate game against Ireland but only featured in the last match against Italy.
Scotland face Canada, the USA and Argentina next month.