This again?
Done before and I doubt anything new will be presented here.
But alright, I'll play (out of boredom on a Monday afternoon):
It depends entirely (duh) on how you define the term. But you shouldn't define it as "any player who was bloody good while playing for Manchester United". You shouldn't even define it as "any player who was arguably the best player in the world while playing for Manchester United".
The only possible chance Ronaldo has to make it as a "United legend" is if you place him in the Cantona category, i.e. a player who arrived and proved to be a catalyst on the pitch/the dressing room and/or an obvious symbol of a monumental change taking place.
In my opinion Ronaldo doesn't really make the grade in either above sense. We didn't transform into anything we hadn't been before (in very recent memory, at that, and under the same manager/within the same overall continuity) - and he wasn't a catalyst on the pitch in the Cantona sense either. He was "just" extremely good. Which means exactly that - he was extremely good, but that doesn't make you a "legend". United have a rich history, we're not short on players who were both extremely good AND who qualify for "legend" status in other ways.
If Charlton is the benchmark, Ronaldo comes up short in pretty much every way.
But he also comes up short compared to Cantona. Or Duncan Edwards. Or Gary Neville (who never had a fraction of Ronaldo's talent - and never was anywhere near him in terms of actual quality on the pitch).
People tend to confuse overall quality with "legend" potential. Jaap Stam has been mentioned already: He was a superior player to almost any United CB in history. He's clearly much less of a "United legend" than Steve Bruce, though.
