After being bought as cover for Patrice Evra, the defender has already admitted he is pleased with his first months in Manchester.
"Alexander has made a great start," van Nistelrooy told ManUtd.com. "He needs a bit more time as he's definitely somebody for the future.
"He's been getting games in the Champions League. For him, it's a dream come true. He's got the ability and needs to learn to obtain more experience and he's definitely somebody to look out for."