Ronaldo has scored 18 goals in all competitions this season since returning to Old Trafford last summer.
But the 37-year-old isn't in line to win anything, with the Red Devils just fighting for Champions League qualification.
A swift exit could be on the cards should Man United fail to secure their spot in next season's Champions League, with Garth Crooks talking up a blockbuster move to America.
He reckons the Portugal international would create a 'formidable partnership' with Beckham and claims playing in the States would give him 'purpose' in his life.
"Old age comes to us all but its impact can be more visible in some than others," he told BBC Sport.
"Ronaldo has scored an impressive 18 goals in 32 matches in all competitions this season but it is a far cry from his usual high standards of almost a goal every game when he was playing for Real Madrid.
"I am a huge admirer of Ronaldo.
"His professionalism is beyond reproach and he has more than fulfilled the expectations required of a 37-year-old player in the toughest league in the world."
Crooks added: "However, he is still a young man who needs a purpose in life.
"The United States might be the place to establish that purpose.
"David Beckham and Ronaldo would make a formidable partnership in Miami.
"One thing is for sure, the five-time Ballon D'or winner doesn't need the money."
Beckham has been hellbent on signing a high-profile star for his Miami-based team, with the former Man United and Real Madrid superstar thought to be eyeing Lionel Messi.
He's also looking at Luis Suarez, with Crooks tipping Ronaldo to make the move across the pond.
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