And a talkSPORT pundit fully understands why, claiming the 37-year-old will not want to stay at Old Trafford for another year of failure.
Having initially been excited by a fresh start under new manager Erik ten Hag, reports in Portugal and Spain claimed Ronaldo is now doubtful any progress will be made due to the club's lack of transfer activity.
It has been rumoured over the last week that the forward is not happy at Old Trafford thanks to the club's quiet summer window since Ten Hag's appointment.
Now it's reported by both Record in Portugal and AS in Spain that he will push to leave the club this summer, just one season into his two-year deal.
United are said to be chasing multiple top targets, including Barca midfielder Frenkie de Jong and several Ajax players, but no deal has been struck yet.
Meanwhile, rivals Liverpool and Man City have both strengthened, and Ronaldo reportedly sees it as a sign it will be another trophyless season again at Man United.
Record claim Ronaldo 'fears Ten Hag doesn't have weapons to fight for titles', and 'doesn't want to waste' the final years of his legendary career at a club where he feels he can't add to his trophy haul.
The report from AS also suggested Bayern Munich as a possible next destination for Ronaldo, where he would replace Robert Lewandowski after Barcelona finally submitted a £34million bid for the Polish goalmachine.
Sky Germany have since claimed the Bundesliga champions aren't interested.
Bayern would be an obvious choice, though, should Ronaldo seek one last transfer to boost his trophy cabinet before hanging up his boots.
The Bavarians have won ten straight Bundesliga titles and regularly challenge for European and domestic honours, and the signings of Sadio Mane from Liverpool and possibly Ronaldo from Man United too would surely see them push to maintain their dominance in Germany this season.
The report in Record adds that Ronaldo has issued an ultimatum to United - 'up your game or I'll leave'.
And that's a stance talkSPORT pundit and former England international Trevor Sinclair understands, saying there's no reason for the Portuguese hero to stay at Old Trafford.
He told talkSPORT Breakfast: "Manchester United want to keep Ronaldo, Ten Hag wants to work with him, but at the moment Ronaldo is looking at the squad and thinking, 'why would I want to stay?'
"This squad is not going to get anywhere near the top four.
"He's not going to join a club bigger than Manchester United, but what he will do is score goals wherever he goes.
"This might be the year where he says, 'You know what, I've loved running the show in European football for the last 20 years, I might want to go over to America and enjoy my life'.
"I'm not saying that is the case, but why would you want to be at Manchester United with the current squad they've got, fighting against top, top teams and getting beat left, right and centre?
"I don't think Ronaldo wants another year like that, and I think he's right to be agitated and putting a bit of pressure on Manchester United."
This news comes after Ronaldo admitted he was excited for Ten Hag's United overhaul, but said the Dutchman 'needs time'.
However, it now appears his patience is wearing thin.
"What I know about Ten Hag is he did a fantastic job for Ajax, that he's an experienced coach, but we need to give him time," Ronaldo told the Man United website following the new manager's appointment.
"Things need to change the way he wants. I hope we have success, of course, because, if you have success, all of Manchester is going to have success as well. I wish him the best.
"We are happy and excited, not only as players, but the supporters as well. I wish him the best and let's believe that, next year, we are going to win trophies."