The pair have been added to the squad after Celtic pair Kieran Tierney and Leigh Griffiths dropped out. The Celtic striker was favoured to start the match up front for Gordon Strachan’s side, but pulled up with a hamstring injury in the recent victory over Aberdeen.
Crystal Palace midfielder James McArthur and Kevin McDonald from Fulham have also dropped out of the squad.
Watt has one cap for Scotland, which he received after coming on as a substitute in the 1-0 victory over Czech Republic in March.
Wallace hasn’t played for the national team since November 2013 and though he was initially selected for the double-header against Italy and France earlier in the summer, the Rangers left back omitted himself from the squad.