Cardiff's Marshall has recorded two clean-sheets and was magnificent as the Dark Blues survived a barrage in Molde before completing a 1-0 smash-and-grab victory over the Norwegians on Tuesday.
Scotland boss Strachan said: "I've known David for a long time and he's now got a presence about him that he didn't always have.
"It's not arrogance, it's just a self-confidence. He hasn't changed off the pitch. He's still a very quiet and unassuming man but there is now a presence on the pitch.
"Is he now putting Allan McGregor under pressure for the number one spot? Yeah, I think he is."
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