Ronaldo, 37, has claimed he is prepared to reveal the 'truth' behind his transfer stand-off in a bombshell interview 'in a couple [of] weeks'.
The Portuguese five-timeBallon d'Orwinner, who netted 24 goals across all competitions for United last season, has made it clear he wishes to move to a club that can offer him Champions League football.
Neville, who won three Premier League titles at Old Trafford alongside the forward, insists Ronaldo must speak up and rescue the club from their miserable to start to the new campaign.
He posted: "Why does the greatest player of all time (in my opinion) have to wait two weeks to tell Manchester United fans the truth? Stand up now and speak.
"The club is in crisis and it needs leaders to lead. He's the only one who can grab this situation by the scruff of the neck!"
The tweet comes after it was previously revealed that United refuted claims the could would cancel his contract if the player's atttitude deteriorated.
Ronaldo, did, though, reply to a fan account on Instagram, accusing the media of 'telling lies'.
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He even claimed he has been keeping a tally of articles about him and only five out of 100 were accurate.
In his post, Ronaldo wrote: "They know the truth when they interview in a couple weeks. The media is telling lies.
"I have a notebook and in the last few months of the 100 news I made, only 5 were right. Imagine how it is. Stick with that tip."
Ronaldo was absent for the majority of the Red Devils' pre-season following speculation over his future, having been away due to 'family reasons'.
He has since featured in both games so far this campaign, coming on as a substitute in the 2-1 home defeat to Brighton, whilst playing the full 90minutes in the 4-0 thrashing to Brentford.