Rosler revealed he challenged the talented 20-year-old to show he can mix up his game.
He said: "I told George before kick-off 'you've shown me you're a good player, now show me you can tackle and head the ball'.
"He did that in an impressive way, both in possession and without it.
"He's still a young player, so we have to make sure his feet stay on the ground, but his start so far has been very promising.
"It's exciting to see players like George with us."