The United manager believes that if both his star strikers can pass the 20-goal mark this season, Manchester City's grip on the Premier League crown will be short-lived.
"I always say this, if you can get two or three goal scorers with over 20 goals, you are definitely in business and you should be challenging for everything," Ferguson told ESPN.
"At the moment I think Wayne Rooney is still to find his goal-scoring form.
"He missed the start of the season with his fitness which was not great, then he had tonsillitis and missed a couple of games.
"When we get through December we will find that Wayne will weigh in with a few goals.
"When Robin came he hadn't played any games so the fitness situation wasn't ideal, but he weighed in with goals and that was a real bonus for us and he is getting better and better all the time.
"He has a fantastic football brain, that is the one thing that we knew when we were going for him that here is a mature player with a great football brain.
"Strikers are rare birds because they only think about goal scoring as their main aspect of life.
"If they are not scoring then they think they are playing terrible, and when they are scoring they are the kings of the castle, its two ends of the spectrum with them. I was a striker myself and I was exactly the same."