Ronaldo finally put pen to paper on his new Red Devils contract on Thursday, ahead of making his second debut for the Premier League giants this weekend.
The Portugal captain, 36, completed a sensational move back to United on transfer deadline day, rejoining from Juventus for an initial £12million.
He has signed a two-year deal with his former club, with the option for a further year.
But, speaking after signing on the dotted line, Ronaldo hinted he could stay for even longer in news that will delight already celebrating fans.
During his first six-season spell at Old Trafford, Ronaldo helped Sir Alex Ferguson's side secure the Champions League and three Premier League titles before moving on to Real Madrid in 2009.
He is still in the shape of his life and became the top scoring international player in history last week by hitting a late brace for Portugal to seal a dramatic victory against Ireland.
And the 36-year-old clearly has no plans to hang up his boots anytime soon, as he hinted he could still be a United player when he reaches the big 40.
"This is why I am here," the ex-Real Madrid man said when asked what his trophy ambitions were in an interview with the club's official website. "I am not here for a vacation.
"Before was good, winning important things and I wore the shirt before, many years ago, but I am here to win again.
"I am capable, me and my team-mates. I am ready to go, I am ready to go. It is a good chance for me, for the supporters, for the club, to get one step ahead.
"I am ready and I think I will be a huge thing in the next three or four years."
Arsenal legend Ray Parlour reckons Ronaldo has all the tools to play until he's 40 - just like Ryan Giggs did.
"Imagine people like Mason Greenwood, looking up to Ronaldo and training with him," he said on Friday's talkSPORT Breakfast.
"I feel a little bit for Bruno Fernandes as he won't be taking free kicks or penalties.
"He's going to be a revelation, I'm sure. I reckon he'll play until 40.
"We saw Ryan Giggs do it but I reckon he'll have to play a bit of a different role. He's not going to be as mobile as he is when he was younger.
"But he's still in phenomenal shape. I reckon at the medical all he had to do was take his shirt off!"
Wayne Rooney, who formed a devastating partnership with Ronaldo in his first United spell, echoed the sentiments of Parlour.
Rooney played with both Ronaldo and Giggs during his career at Old Trafford and is confident CR7 will emulate the longevity of the United icon's career at the very top level.
"The last time he played here, he was more of a runner, a great dribbler, with pace and power," Rooney told Reuters.
"Whereas now, he's a goalscorer. I think his game has adapted dramatically.
"His ability is obviously one thing, but then he's also looked after himself massively … he's still in great condition. It wouldn't surprise me if he's playing until he's 40, like Ryan Giggs did, and still scoring goals.
"His team-mates will have to work a little harder. But if it's anything like last time - towards the last two years of playing with him - the team allowed him to do that because he scores you goals, and goals win you games."
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