Scotland have called up Tony Watt and Lee Wallace after Celtic's Leigh Griffiths and Kieran Tierney dropped out of the squad to face Malta.
Midfielders James McArthur and Kevin McDonald also dropped out before the opening World Cup qualifier on Sunday.
Hearts forward Watt, who has scored once this season, has one cap, while Rangers left-back Wallace has eight.
Striker Griffiths came off injured after scoring in Celtic's 4-1 defeat of Aberdeen on Saturday.
| Revised Scotland squad | |
|---|---|
| Goalkeepers | Craig Gordon, Jack Hamilton, David Marshall |
| Defenders | Christophe Berra, Gordon Greer, Grant Hanley, Alan Hutton, Russell Martin, Callum Paterson, Andrew Robertson |
| Midfielders | Ikechi Anya, Barry Bannan, Oliver Burke, Darren Fletcher, James Forrest, John McGinn, Barrie McKay, James Morrison, Matt Ritchie, Robert Snodgrass |
| Forwards | Steven Fletcher, Chris Martin, Steven Naismith, Tony Watt |
The 26-year-old netted 40 times last season and has seven goals so far this term but has yet to score in seven appearances for Scotland.
Steven Fletcher, yet to score for new club Sheffield Wednesday, was Scotland's main striker in their unsuccessful Euro 2016 qualifying campaign, while Chris Martin and Steven Naismith also featured in attack for Gordon Strachan's side.
That trio and Watt make up the forward contingent of Strachan's revised squad.
Midfielder Robert Snodgrass is optimistic about being fit, despite a painful collision with a goalpost during Hull City's defeat by Manchester United at the weekend.
It will be Scotland's first game since midfielder and captain Scott Brown retired from international football.
West Brom's Darren Fletcher - a former national team skipper - could resume the armband duties.
Strachan's pool also includes winger Oliver Burke, who joined German side RB Leipzig from Nottingham Forest on Sunday in a £13m deal - making him the most expensive Scottish player.
| Scotland's 2018 World Cup qualification fixtures | |
|---|---|
| 2016 | 2017 |
| 4 September: (a) v Malta | 26 March: (h) v Slovenia |
| 8 October: (h) v Lithuania | 10 June: (h) v England |
| 11 October: (a) v Slovakia | 1 September: (a) v Lithuania |
| 11 November: (a) v England | 4 September: (h) v Malta |
| 5 October: (h) v Slovakia | |
| 8 October: (a) v Slovenia | |