"Graham's a top man," midfielder Greening told the WBA website. "He has come down from Scotland as a young boy and done really well in training.
"In recent games, he has come on and made an impact. He gets on the ball and can take players on and create things. He's only 21 and has got a really bright future.
"There is a lot of expectation on him but I think he can produce given his chance.
"He can take players on and can play left, right or central midfield - similar to me. The more he plays, the better he can become.
"Since joining us, he has already improved immensely through playing with better players.
"He wants to work hard and when you've got that you have always got a chance."