With Brown suspended for going over the disciplinary points threshold, Armstrong took over the captain’s armband for Saturday’s game, which Celtic won 4-1 thanks to a double from Patrick Roberts and goals from substitutes Scott Sinclair and Callum McGregor.
Armstrong has often been gently teased by his team-mates for his well-spoken nature and interest in studying law in his spare time.
Asked what Armstrong’s huddle speech was like, goal-hero Roberts couldn’t help but poke fun.
Roberts said: “It was all right. He’s a little posh boy, so it was quite posh. Nah, it was good. It was a good speech.
“Obviously it wasn’t Broony, but all the boys out there are leaders and we got the performance.
“There were a few more big words that I couldn’t understand. But the main thing was to win the game.”