"Rooney is just awesome, isn't he? He is one of the best players in the world - if not the best - even at his young age," said former United midfielder Greening.
"It's very hard to pick him, either in the hole or when he drifts wide or drops off. He's fast and he's strong. I don't think there's a weakness in his game. It simply doesn't matter where Alex Ferguson decides to play him. You've just got to let him play where he feels he will be effective.
"If he is getting joy down the left, he'll go there and if he's getting joy down the right, he'll go there. If he's getting joy in the hole, he'll play there. He's just an amazing player.
"I watched him play for England in midweek and he was awesome. There's just no stopping him at the moment.
"In the world today you've got players like Lionel Messi, who is truly a great player. But we're lucky in England to have a player like Wayne Rooney because he's somebody who can change a game, a bit like Gazza did.
"Of course the scary thing about Wayne is he's still only 22, so his best years are still ahead of him.
"They say you don't hit your best form until you're 27 or 28 so I dread to think what he'll be like when he's that age.
"Wayne's workrate has always been outstanding. At the moment he's hitting tremendous final passes and scoring goals too. The thing is, in a team like United's, he's just going to go on learning and keep getting better.
"He's going to be some player in four or five years' time!"