Van Nistelrooy netted 150 goals in just 219 games for United between 2001 and 2006 and believes the former Arsenal striker (whose current strike-rate almost mirrors Ruud's 0.68 goals per game) can score just as many.
"I hope so," he told manutd.com. "My time has gone and now others have taken over, so I hope he does [score as many as me].
"Robin has proved he's fitting in easily. It's like he has always played for the club.
"He didn't need any time to settle in. He was straight on his level, scoring important goals and winning games for the team."
Van Nistelrooy is confident Sir Alex Ferguson will help Van Persie thrive at the club.
"I think he will," Ruud said. "That is what the manager does: he makes you feel strong and gets the best out of people.
"Robin's style – the way he wants to play, the way he likes to play – fits United so well. I'm happy for him that he’s made such a great start because he deserves it. He’s a great player and I hope he can continue like this for a long time.
"It’s not just scoring goals, either. He's great in his ability to get involved in the play as well as his finishing, which is fantastic."