The Celtic winger has been discussing his 22-year-old team-mate.
The Bhoys were dumped out of the Europa League with no wins to their name from five European games following a 2-1 defeat to Ajax.
Most of Celtic's first-team stars failed to stand up and be counted but McGregor performed well and netted for Ronny Deila's men.
Armstrong, meanwhile, says he sees the 22-year-old's quality in training every day and hopes he gets the chance to 'kick on' after his encouraging European display.
Armstrong told the Celtic site: "I see every day in training that Callum is such a good player. He is good with both feet and very skilful, so I’m very pleased he has managed to get a goal tonight and hopefully he can kick on."
Celtic travel to Inverness Caledonian Thistle for their next Scottish Premiership clash on Sunday afternoon and will now approach all of their domestic games in the knowledge that is all they have on the table.
Following their failure to claim the treble last season - and their subsequent failure in Europe - Deila's side will no doubt make it their mission to claim all three domestic trophies this season to compensate.
Should they fail to do that, further questions will no doubt be asked of the club, manager and players.