The Dutch striker, 29, has smashed 13 goals in 19 games since his £22million summer switch from Arsenal to Old Trafford.
Van Persie, who faces City at the Etihad tomorrow, said: “I made my mind up very quickly and I am coming into work with a big smile on my face every day.
“It is not really work, it is my hobby — I love football.
“But everyone has been so nice to me and I have been having the time of my life here.
“So I don’t regret that — but of course in a derby you have lots of people involved — the fans and the players.
“Everyone is really committed and wants their team to win and we’ll do all we can to win too.”