The 21-year-old is eligible for both Scotland and England, with his emergence under Jose Mourinho leading to much conjecture over which nation he should choose to play for.
Lancaster-born McTominay has previously stated he sees his international future with the country of his father and reportedly pledged to represent Scotland this month following a meeting Alex McLeish.
And he is in line to make his debut for Scotland after McLeish included him as one of six new faces in his first squad since being re-appointed as manager in February.
Jon McLaughlin, Barry Douglas, Dylan McGeouch, Scott McKenna and Oliver McBurnie also receive their first call-ups.
Scotland face Costa Rica on March 23 at Hampden Park before travelling to Budapest to take on Hungary four days later.
McLeish was appointed for a second time after Gordon Strachan was unable to lead them to the World Cup finals. Scotland have not featured at a major tournament since the 1998 World Cup, where they were eliminated in the group stage.
Scotland squad: Jordan Archer (Millwall), Allan McGregor (Hull City), Jon McLaughlin (Hearts); Barry Douglas (Wolves), Grant Hanley (Norwich City), Russell Martin (Rangers), Scott McKenna (Aberdeen), Charlie Mulgrew (Blackburn Rovers), Callum Paterson (Cardiff City), Andy Robertson (Liverpool), Kieran Tierney (Celtic); Stuart Armstrong (Celtic), Tom Cairney (Fulham), James Forrest (Celtic), Ryan Fraser (Aberdeen), Kevin McDonald (Fulham), Dylan McGeouch (Hibernian), John McGinn (Hibernian), Callum McGregor (Celtic), Kenny McLean (Aberdeen), Scott McTominay (Manchester United), Jamie Murphy (Rangers), Matt Ritchie (Newcastle); Ryan Christie (Aberdeen), Jason Cummings (Rangers), Oliver McBurnie (Barnsley), Matt Phillips (West Brom).