Van der Gouw worked with Buttner at Vitesse Arnhem and is delighted for the young left-back over his move to United.
"If he can play plenty of games then people will love him because he gives absolutely everything," van der Gouw told ManUtd.com. "Don't worry about that; he'll never let you down.
"He's scored a few goals, but that's because he started out as a left midfielder. He only became a left-back in the last couple of years, but he made such big progress that it became his position.
"He still likes to go forward and try to score. He has a powerful kick, a very good left foot and he puts in some good crosses, too. He has a lot of energy and he's good for team spirit."