The Belgian spent over five years at Old Trafford before moving to China last month.
He told Het Nieuwsblad, “My first season in Manchester was difficult, but I left as a respected player.
"I gave my very best for this club, played so many games and almost only scored important goals.
“I worked with super players and managers at one of the biggest clubs in the world. Then you can only look back with a smile.
“I really don't have a favourite (manager). David Moyes or Louis van Gaal. I learned something from every manager."