Gray has 65 caps, including one for the British and Irish Lions, with his last appearance for his country coming against England in the 2017 Six Nations as he battled with a long-term back injury for much of last year.
Better news for Scotland is that scrumhalf Greig Laidlaw has returned from injury and came through two outings for French Top-14 side Clermont Auvergne unscathed.
He will battle with incumbent Ali Price for a starting berth at the Principality Stadium on Saturday, with one of the major talking points ahead of the clash focusing on who coach Gregor Townsend will entrust with the number nine jersey.
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Scotland's last international was a record 53-24 victory over Australia in November, while they ended a nine-game losing streak against Wales in last year's Six Nations.
They have not won any of their last eight visits to the Cardiff though, with their previous victory a 27-22 success in 2002.
(Reporting By Nick Said; Editing by Christian Radnedge)
