Norwich City centre-back Grant Hanley will miss Scotland's final two World Cup qualifiers due to a groin injury.
Having been substituted near the end of Norwich's defeat to Leeds last weekend, the 29-year-old has now been ruled out for "two to three weeks" by his club.
Bar the 3-2 win over Israel, for which he was suspended, Hanley has started every game in the World cup campaign and was an ever-present at Euro 2020.
However, fellow defender Kieran Tierney has handed Scotland a fitness boost.
The 24-year-old has missed Arsenal's last three games with an ankle problem, but is back training and in contention to face Watford on Sunday.
Both players were named in Steve Clarke's 25-man squad this week.
Scotland, who need one point to secure a play-off place for the World Cup in Qatar next year, conclude their qualifiers away to Moldova away next Friday and against Denmark at Hampden three days later.