Celtic defender Greg Taylor will be sidelined for Scotland’s Nations League matches against Croatia and Portugal.
The 26-year-old left-back missed Sunday’s victory at Ross County due to a calf injury sustained during the midweek Champions League defeat to Borussia Dortmund.
Taylor, who has earned 14 caps, also withdrew from the squad for the initial defeats to Poland and Portugal in this campaign.
Head coach Steve Clarke is already missing 10 players due to injuries, and there are concerns regarding goalkeeper Angus Gunn.
The Norwich City keeper was substituted at half-time against Hull City on Saturday after sustaining a heavy blow to the ribs.
Vice-captain John McGinn is among those unavailable, leading to the first-time call-ups of Nicky Devlin, Liam Lindsay, and Andy Irving.
Scotland will travel to Zagreb on Saturday before hosting Portugal three days later.
Portugal currently leads Group A1 with six points, followed by Croatia and Poland with three points each, while Scotland has yet to earn any points.