The 29-year-old was reportedly of strong interest to City but opted for Sir Alex Ferguson's side.
City's own strikers have failed to match their standards from last season but Mancini claims missing out on Van Persie is not something that bothers him.
The Italian said: "No. In this moment, it is in the past, this.
"We have good players. If we improve this situation - in this moment we don't score a lot of goals - I am sure if we continue to work we can improve."