Ronaldo is a world class player, so going to Roma is so underrated for a player like him, if Ronaldo decide to move form Manchester United, he should be going to a Good and competitive team. Perhaps, Ronaldo is not happy with the club, the team is not performing up to his expectations, their last season performance was one of the worst performance in United history. But with the new management, I think we will see a different performance this season, cause the new coach is putting in his efforts to bring the best out of the team. So I will suggest that he stay at the team, instead of going to Roma, he should give the new management a chance.
Actually in this case there is no reason for Ronaldo to leave especially for Roma.
Even though it's the worst possibility now that Ronaldo has moved from MU, it's clear that his choice is not Roma.
The reason is quite clear, he wants to gain experience and doesn't want to be separated from the Champions League and Roma certainly can't do that so why would he leave if he still can't be in the Champions League.