Sunderland's Ross Stewart and Hearts' Craig Halkett have been called up by Scotland for the first time.
St Johnstone goalkeeper Zander Clark will also join the squad to replace the injured David Marshall.
Stewart has scored 22 goals in 38 games for the English League One side this season.
Halkett will cover central defence after Scott McKenna withdrew, with Liam Cooper and John Souttar sidelined.
Both first-time call ups could make their debut in the friendly with Poland on Thursday, with Scotland then playing either Austria or Wales the following Tuesday.
Meanwhile, captain Andy Robertson is a doubt after missing Liverpool's FA Cup quarter-final win against Nottingham Forest with illness.