United and City locked horns for Van Persie's signature after the Dutchman decided to leave Arsenal with the striker deciding to make the move to Old Trafford.
City chief Roberto Mancini has claimed United's signing of Van Persie has been the difference in the title race this season, feeling things would have been different if he managed to bring the Dutch ace to City instead.
However, Ferguson has aimed a swipe at City by suggesting Van Persie was never interested in joining Mancini's charges.
And Ferguson has paid tribute to Van Persie for making such an important contribution for United in his first season with the club.
"It's hypothetical, he was never going to City," said Ferguson.
"He's been fantastic for us, a really good footballer. We needed a bit of maturity up front and he's been terrific.
"The improvement is not just through Robin but even when he doesn't score he's a fantastic footballer."
As well as missing out on the Dutchman, Mancini failed to land all his prime transfer targets last summer, but with new administration at the club he is confident of doing better this time around.
City did strike one important blow last week when Yaya Toure signed a new four-year contract and spoke of his confidence in the club's future.
Mancini said: "This is important for the club, it is important that they sign new contracts.
"We know that we should buy important players for next year if we want to improve.
"In football you can buy good players and afterwards you don't win - this is football, it is incredible.
"But I am sure we can do well this year, we can do a good job in the market."
Mancini is likely to want to strengthen his squad in a number of areas but is giving little away as to his intentions now.
He said: "I don't know, it is difficult to say this. You may want one player, but maybe two or three teams want the same player and after you can take this or take another player. It is difficult."
The title race may be all but over, but City still want to make a point tonight to prove the gap between them and United is not as large as the table suggests.
Mancini said: "I think we know we can beat them because they are not better than us.
"This is sure, 100 per cent - although they deserve to win this title."