He said of the Scotland U21 midfielder: "James is an all-rounder. As far as going to win the ball and reading where the ball is going to drop, I don't think I have come across anybody better in my career. On the ball, he can pick passes and can go forward and defend.
"It is in his own hands, but I think that, if he keeps progressing as he has in the last three years, the sky's the limit for him. James is the type who, if you win the game and he is not playing well, he is still not happy."