Whilst United are sticking to their stance of not making an official bid for the 25-year-old, it has been claimed a fee has been agreed with Chelsea, which would allow the transfer to proceed.
Press Association Sport understands the deal is moving apace, with a source close to the deal indicating it was not far off being concluded.
Given the rapid movement of the transfer - likely to be around the £40million mark - Mata could be a United player in time to face Cardiff at Old Trafford on January 28.
Mata is thought to have missed training on Wednesday and is said to have indicated to friends he was destined for Old Trafford.
A move for the Spain international would make sense from virtually every angle.
Although Gary Neville pointed out earlier this week his arrival would represent a change of tactic for United, who have traditionally relied upon two wingers, the knowledge that none of Antonio Valencia, Ashley Young and Nani have sparkled under Moyes this season means ditching the concept would not be a hardship.
In addition, it would prove to United fans their club was serious about addressing the sharp decline in fortunes experienced since Sir Alex Ferguson's departure, even if it cannot guarantee the Champions League spot they crave.
Speaking on Sky Sports 1 on Wednesday evening, Neville said: "This is a number 10 who plays in a wide area, and I'm imagining that Robin van Persie and Wayne Rooney would take up the predominant roles, but he's a huge talent.
"He can spot a pass. They've lacked creativity at times Manchester United in the final third and he definitely has that.
"I think that this is a big transfer window for them. If they can pull in a big signing it would lift (executive vice-chairman) Ed Woodward, it would lift the fans and it will give everybody at the club a boost. They need that here."
For Mata, it would end a tortuous few months, where he has left Jose Mourinho unimpressed and become increasingly marginalised, thereby enhancing his chances of making Spain's World Cup squad.
Chelsea would bank a far larger fee than they could hope to attract from Mata's other suitors - Barcelona and Paris St Germain - and whilst it would be unusual for them to sell to a fellow Premier League giant, Mourinho knows United are not a threat in this season's competition.
Indeed, given United have played Chelsea twice but must still encounter Arsenal and Manchester City in the run-in, it could be argued Mourinho is strengthening his own team's position.
For Moyes, it can only be the start of what is sure to be an extensive rebuilding programme, that is not likely to be completed for another 18 months, with the Scot adamant he is not prepared to rush his work.
"I fully understand that supporters are keen to see us freshen up the squad with new faces, but January is a difficult month in which to bring people in," Moyes told United Review ahead of Wednesday's Capital One Cup semi-final with Sunderland.
"While we are actively scouting players all the time, a lot of the work we are doing now is preparation for the summer.
"If we can do any business now then we will certainly try to do it, but I will not comprimise the standards required for a player that can come into this club and help improve it."