Widespread reports in the press this morning suggest that Red Devils officials have been informed Rooney will not sign a new contract and wants out of the club, which would leave them with little option other than to cash in on their most valuable asset.
There has been plenty of speculation about Sir Alex Ferguson's relationship with his star striker since stories about the 24-year-old's private life first surfaced at the beginning of last month.
Rooney appeared to make a direct challenge to Ferguson's authority on Tuesday after England's Euro 2012 qualifier with Montenegro, when he went out of his way to contradict the Scot's claim that he has been suffering from an ankle injury.
United's reaction to newspaper suggestions that Rooney could quit the club were swiftly countered yesterday. "To suggest Wayne Rooney will be sold in January is nonsense," said a club spokesman.
Ferguson has so far avoided any meaningful public discussion about Rooney's situation but appeared to deliver his own verdict when he left the forward out of his starting line-up for Saturday's Premier League encounter with West Brom, then brought him on as a substitute with 19 minutes remaining and told him to play on the left wing.
Although it was interpreted as the final straw by some, Rooney's relationship with Ferguson soured some time ago. Talks over a new contract have stalled and there is no intention from the player's side to re-open negotiations.
It will come as a shock to many observers to discover the extent and speed of the breakdown, given it was only last season that Rooney scored 34 goals for his club. Even though Rooney's form this season has been well below his normal high standards - his only goal, against West Ham in August, came from the penalty spot - he remains a crowd favourite.
United do have the option of sitting tight and hoping for a thaw in relations. However, they are acutely aware Rooney's value will plummet if he does not leave in January and 12 months after that he would be free to sign pre-contract terms with any club on the continent, and leave on a Bosman free transfer in the summer of 2012.

The Glazer family are unlikely to be keen on that idea, which is why the prospect of Rooney leaving midway through the current campaign has taken hold.
And the United boss is due to address the media on Tuesday, prior to his side's Champions League encounter with Bursaspor at Old Trafford, with questions sure to focus on the reports.