Callum McGregor: Celtic midfielder called up for Scotland qualifiers
Callum McGregor has been called up by Scotland after scoring both goals as Celtic preserved their unbeaten domestic record on Saturday.
Scotland boss Gordon Strachan has drafted the 24-year-old into his squad for the World Cup qualifiers against Slovakia and Slovenia.
He has now scored six goals in 15 appearances this season.
However, midfielder Matt Ritchie has withdrawn from the squad.
Ritchie played the full 90 minutes in Newcastle's 1-1 draw with Liverpool on Sunday.
McGregor's double salvaged a point for the champions in a 2-2 draw with Hibernian at Celtic Park.
Skipper Brown has a hamstring problem while Armstrong has calf trouble.
Speaking after Saturday's game, McGregor was asked by BBC Scotland if he expected to hear from Strachan.
"I don't think so," he said.
"The manager has picked his squad. All I can do is my bit on the pitch for Celtic. If the call comes then great, but I think he is happy with his squad.
"All I can do is keep performing for Celtic, try to come up with goals and assists and play well. That is my main focus, and anything after that is a bonus."
Scotland face Slovakia at Hampden on Thursday and visit Slovenia on Sunday.
Revised Scotland squad for qualifiers against Slovakia and Slovenia:
Goalkeepers: Jordan Archer (Millwall), Craig Gordon (Celtic), Allan McGregor (Hull City)
Defenders: Ikechi Anya (Derby County), Christophe Berra (Heart of Midlothian), Grant Hanley (Norwich City), Liam Cooper (Leeds United), Charlie Mulgrew (Blackburn Rovers), Andrew Robertson (Liverpool), Kieran Tierney (Celtic), Steven Whittaker (Hibernian)
Midfielders: Barry Bannan (Sheffield Wednesday), Darren Fletcher (Stoke City), Ryan Fraser (Bournemouth), James Forrest (Celtic), James McArthur (Crystal Palace), John McGinn (Hibernian), Callum McGregor (Celtic), Matt Phillips (West Bromwich Albion), James Morrison (West Bromich Albion), Matt Ritchie (Newcastle United), Robert Snodgrass (Aston Villa, on loan from West Ham United)
Forwards: Steven Fletcher (Sheffield Wednesday), Leigh Griffiths (Celtic), Chris Martin (Derby County)