Ronaldo is the all-time record goal scorer in the Champions League, but he won't be playing in that competition if he stays at United next season as they will be in the Europa League.
Portuguese sports daily Record claim Ronaldo wants to leave after only one season back at Old Trafford as he fears new boss Erik ten Hag needs an extended period of time to revive the club's fortunes.
At the age of 37, Ronaldo doesn't have time on his side to wait for that progress, with agent Jorge Mendes reported to be exploring possible escape routes for his star client.
Manchester City, Chelsea, Liverpool, Tottenham are not expected to be options for Ronaldo, but he has been strongly linked with a move to Bayern Munich.
A swap with Robert Lewandowski isn't an option as he either stays or goes to Barcelona, but it appears there are doubts over whether Ronaldo wants to stay at United.
Former United defender Wes Brown is hoping Ronaldo stays at Old Trafford, as he gave his verdict to sundayworld.com.
“Ronaldo has to stay and I can’t see why anyone would dispute that,” declares Brown, speaking to the Sunday World at a Bookmaker.com event in London.
“Listen, people can say whatever they want about him, but he is the complete goal machine. Probably the best at putting the ball in the net of all-time.
“There have been so many times this season when we have not been at our best and he has dug us out of a hole.
“He was massive on some of the Champions League nights, the hat-trick against Tottenham a few weeks back was fantastic and there have been too many games when he has dug us out of trouble. That’s what Ronaldo brings to this team.
“He might be at the back end of his career and he is not the future, but he has got United out of a lot of trouble this season and I think Ten Hag needs to keep him for next season because how can you say United or any team don’t need Ronaldo."