The 31-year-old England forward scored his 250th goal for United in the Premier League on Saturday.
The 31-year-old England forward scored his 250th goal for United when his superb free-kick late on rescued a 1-1 draw away to Stoke in the Premier League on Saturday.
In the process Rooney surpassed the previous record of 249 United goals set by England great and World Cup winner Bobby Charlton back in 1973.
United captain Rooney's future at Old Trafford remains a topic of debate, with the former Everton striker used sparingly by current Red Devils manager Jose Mourinho.
But Ferguson believes Rooney's place in United's history is already secure.
"Well, it lasted for 44 years, I think, and when Wayne Rooney joined the club I could never imagine anybody could beat Sir Bobby's record," Ferguson told MUTV, United's in-house television station.
"So his achievement is outstanding. It's amazing, he's 200-odd games short of Bobby's playing record and that makes it even more amazing," added former United manager Ferguson, who brought Rooney to Old Trafford from Liverpool-based club Everton in 2004.
"I don't think (anyone can overtake Wayne). I couldn't say never -- never say never -- but if you look at modern-day football, Manchester United are one of the few clubs who can keep players for over 10 years.
"But, in the modern day, you see it happening less and less that players stay for that length of time.
"For instance, Jose (Mourinho) mentioned young Marcus Rashford and he's got to score more than 20 goals a season for the next 10 years or so and that is difficult in itself."
Rooney was football's most expensive teenager of all-time when Ferguson signed him from Everton for around £30 million ($37.5 million, 35 million euros).
"The only way you can assess value is the length of time he has been at the club," said Ferguson.
"I was very lucky in my time to have Roy Keane for 11 years, Steve Bruce for a long period, Peter Schmeichel for years, Dennis Irwin, you know?
"The young ones that came through like Ryan (Giggs), Paul (Scholes) and Gary (Neville) lasted more than 10 years," he added. "With the case of Wayne, what we felt at the time was 18 years of age, he had huge potential.
"Hopefully if we have got him for 10 years, £27 million is nothing. It is gone like that... the value was there, no question."