That is the understanding of Goal.com, who claim that Real will sanction his departure if they cannot appease the Portuguese forward who recently claimed to be "sad."
However, it is believed that Real are intent on keeping Ronaldo and talks will be held between the player, manager Jose Mourinho and president Florentino Perez.
Speculation over Ronaldo's future began following his refusal to celebrate after scoring in a La Liga match with Granada and later stated that the club knew the source of his unhappiness.
Reports in Spain subsequently claimed that Ronaldo's discontent was as a result of the amount of money being offered in his contract negotiations.
On Thursday, the 27-year-old attempted to dispel speculation over his future.
"I would like to reaffirm, without being concerned about contracts, that my focus is solely on winning every game and every available trophy with the essential company of my teammates and all Madridistas," he said in a statement, according to ESPN.
Even if Ronaldo were to leave Real, a return to United always appeared unlikely. While Ronaldo still speaks highly of his former boss Sir Alex Ferguson, it is difficult to envisage United's owners spending what would have to be an enormous sum on a player-even of Ronaldo's ability-who will be 28 in February.
It is a similar story for another La Liga star, Cesc Fabregas. The Barcelona midfielder hinted at his discontent with his role at the Camp Nou last week and speculation immediately swirled of a return to Arsenal, as well as possible interest from Manchester United.
However, the Spain international has confirmed that he is happy to remain at his boyhood club.
"I have to do what the coach asks me to and that isn't to score two goals every game. I try to do my job and I'm very calm, very content and very happy to be here," he said, according to the Daily Mirror.
"What I want is to stay and play at Barca and work as hard as I can."
One player who could arrive at Old Trafford in the near future is young Italian striker Domenico Berardi. Reports in recent days suggested United were keeping a close eye on the 18-year-old, who plies his trade for Italian Serie B side Sassuolo.
Now, the general director of the club, Nereo Bonato, has confirmed United's interest.
"The interest from Manchester United? The player is followed with great attention by many clubs, including the Red Devils and also Juventus," he said, according to Sky Sports.
"But there are other Italian and foreign sides who have observed him in recent games.
"For the moment there has been no concrete contact, so we're thinking about the present and how to develop Berardi in the best way."
Bonato suggested that he would not stand in the player's way of joining a major club.
"He has a contract with us until 2015 and if some big club should come forward we will see what is best for everyone."
In other United news, Nani is said to be interesting Italian champions Juventus, according to the Daily Mirror. The Portuguese winger has yet to sign a new contract at Old Trafford and was believed to have been the subject of a £25 million offer from Zenit St Petersburg in the closing days of the transfer window.
The Mirror reports that Juventus will target both Nani and Theo Walcott when the transfer window reopens in January.