The Portuguese superstar has asked the Red Devils to consider offers for him this summer, but they insist that he is not for sale.
And the 38-year-old may have hinted that he could be staying in Manchester with his latest post on social media.
Ronaldo uploaded a photo of him in the gym wearing last season's adidas training shorts, with the caption, 'HARD WORK', despite being a Nike athlete.
This comes after Real Madrid became the latest club to reveal that they won't be signing the six-time Ballon d'Or winner, who spent nine successful years at the Bernabeu.
Real boss Carlo Ancelotti said: "We're not gonna complete any other signing. We're happy with the current team, we're strong".
"I'm happy with Rüdiger, Tchouaméni and I'm sure Hazard will help us a lot."
Chelsea - who completed the signing of Raheem Sterling on Wednesday - are also said to have rejected the opportunity to make an approach for the Man United man, after discussions with boss Thomas Tuchel.
Paris Saint-Germain had the chance to potentially team Ronaldo up with fellow stars Lionel Messi, Neymar and Kylian Mbappe, but they felt he wasn't the right signing at this moment in time.
He was also linked with a move to German champions Bayern Munich with their talisman Robert Lewandowski set to leave the club, but his £500,000-a-week wages mean they also rejected the chance to sign him.
His high wages are also said to be putting off the likes of Jose Mourinho's Roma and Napoli, whilst Sporting Lisbon, another of his former clubs, struggles to see a deal getting done.
The Portuguese is running out of options and may now be stuck at Man United until his contract runs out next year.