Rangers full-back Nathan Patterson has been dealt an injury blow after picking up a knock against Moldova.
The Rangers right-back made his first senior international start on Saturday night in the win at Hampden.
The 19-year-old had seemed like a guaranteed starter against Austria in the crucial qualifier clash after an impressive performance, but was a surprise withdrawal ahead of the trip to Vienna.
Ryan Fraser and Kenny McLean have also been forced to pull out for the national side through injury, with Hibs right-back Paul McGinn brought into the set-up.
It adds to a lengthy list of absentees for Steve Clarke with a series of Covid and injury issues blighting the squad ahead of the trip to Vienna.
The Scotland gaffer said: "Nathan Patterson and Kenny McLean have injuries from the game and Ryan Fraser has picked up a knock in training.
"I had seven or eight doubts after the game on Saturday so losing three is not the worst outcome.
"It's very difficult to call players in because of all the Covid stipulations so we're grateful to Paul for making himself available. He's a good addition."
Despite an ever-growing list of absentees, Clarke remains confident of earning at least second spot in the group.
Ahead of the Austrian showdown, he said: "We want to play well and if we do that we feel we're capable of getting a win.
"The Israel-Austria game has changed the dynamic of the group. Austria will feel they need to win."
