Goode has been in sparkling form for the Men in Black this season both defensively and when joining the back line, and his performances have caught the eye of England coach Stuart Lancaster.
The number 15 made two appearances for England against South Africa in June and McCall insists Goode has improved since the summer.
McCall said: "I think there are two things. First I think the penny dropped for Alex two months ago as to how important his body was and his improvement physically and athletically has been huge.
"He's quicker than he was, he's more powerful, he's stronger and that has given him a lot of confidence.
"And I think that's the other thing - he's always been a great natural talent but I think the two caps in the summer have given him real confidence and he's brought that confidence into this season.
"He's much more of a voice, much more of a leader on the pitch and I think that's what perhaps swings it for him for England."
Goode is preferred in the England line-up to fellow full-back Mike Brown of Harlequins, a decision McCall believes is down to Goode's ability going forward.
"I think Brown's a great full back too but Alex gives something a little bit different from Brown in terms of what he sees and the voice that he has", McCall explained.
"Alex has a high skill set and he's a very, very talented player. He's a lot quicker than people think now as well but he does see things early like a fly half - he can step in to that first and second receiver role which I think Stuart’s keen on too."