Ronaldo missed the majority of United’s pre-season preparations after handing in a transfer request last month.
The 37-year-old, who has a year left on his current deal at Old Trafford, made his first appearance under Erik ten Hag in last week’s draw with Rayo Vallecano.
Ronaldo’s former United teammate Rooney believes now is the right time for the Red Devils to part ways with the five-time Ballon d’Or winner.
“I think United should let Cristiano Ronaldo go,” Rooney wrote in his column for The times.
“It’s not that Ronaldo can’t play in a Ten Hag team. He can play in any team. Ronny will always score you goals. But my personal view is that United are not ready to challenge for the title now, so the goal is to build a team that can win the league in the next three to four years, and you have to plan for that.
“If the reports are true that Cristiano wants to leave the club, then United should allow him to go and take the No.9 for who will be there for the next three or four years and really help them build a team that can Ten Hag should be given time to do that.”
“Ronaldo’s achievements in football have exceeded anything anyone could have wished for and imagined,” Neville said. Sky Bet’s The Overlap.
“He will go down as one of the greatest players of all time and always will be. What happens this summer at Manchester United will be forgotten in 20 years.
“But it’s unpleasant for me to watch as a former Manchester United captain, thinking that at the moment the star in the dressing room is playing.
“It’s happened at times over the last few years where you’ve had it [Paul] Pogba’s agent – not necessarily Pogba – but his agent is always playing.
“You can’t have your star at a club running the shop. You can’t have that. So when Sir Alex Ferguson has promoted players in the past, it’s because that player had to move on.
“I know Manchester United fans want Ronaldo to stay. But if Ronaldo wants to leave, Manchester United – in my mind – should make it easier.”
It is not clear whether Ronaldo will play for United in their Premier League opener of the new season against Brighton on Sunday.
But coach Ten Haag says he is happy Ronaldo is still part of his squad.
“How do I feel to start the season with Ronaldo? I’m very happy,” said Ten Haag.
“I told you before: we planned with him for the season. We have a top striker and I am very happy that he is here, he is in the team and we are sticking to the plan.”