As Nik Simon of the Daily Mail reported on Saturday (Jan. 25), the Spaniard arrived at the club's Carrington training ground for a medical, the last of the fine details needed before a £37 million transfer is completed.
However, it's not good news for all at Old Trafford, with a number of members on the playing staff set to have their chances affected as a direct result of the latest acquisition.
Here, we discuss those who promise to lose out most once Mata's move is made official.
Though not the most directly affected in terms of position, Danny Welbeck's chances of first-team football have the potential to be damaged in Mata's stead.
Talk of a front four at Old Trafford involving the Spanish playmaker, Adnan Januzaj, Wayne Rooney and Robin Van Persie has got tongues wagging in recent days, but there's been no mention of the homegrown product Welbeck.
This season has been one of the English youngster's more fruitful campaigns with his boyhood club, seeing him score eight times in 12 Premier League starts, per Transfermarkt.
However, with a rejuvenated Van Persie back in the squad, Rooney in behind him and the duo of Januzaj and Mata out wide, it becomes slightly foggier as to where Welbeck fits in.
Even with a fit RVP, Welbeck has been able to fill in on the wing, but another burgeoning member of the flanks promises to obstruct the forward further, even in his secondary position.
Perhaps the most talked-about United player likely to be hurt by the incoming signing is misfit Shinji Kagawa, who has infamously struggled to fit in at Old Trafford even without the two-time Chelsea Player of the Year being present.
In many ways, the Japanese midfielder is a very similar asset to Mata. Both players function well as a No. 10 or in a trequartista role playing just off the main striker, but are far from incapable of starring out wide.
Kagawa has found his forays from the left wing to be largely ineffective, however, and the ongoing project of finding some way to slot him into a more favoured central role have come out empty up until now.
On Jan. 24, Goal.com's Sam Lee reported Kagawa's agent Thomas Kroth as saying that his client will not be leaving Old Trafford, irrespective of Mata's move, but it certainly doesn't benefit the 24-year-old's hopes.
With Rooney enjoying arguably his best season to date playing in behind Van Persie, the right side of midfield would seem Mata's most logical point of introduction under Moyes.
The New York Times' Jerrad Peters agrees that the right flank is for Mata:
A role that he's used to occupying from his days with Chelsea and Valencia, the trickster's main competition for the spot will be Antonio Valencia (all too coincidentally).
The Ecuadorian international has been fairly productive this term, scoring four goals and making three assists across all competitions, per Transfermarkt.
That being said, it's hardly a rate that will warrant Moyes to be concerned about dropping Valencia from the line-up, with Mata starting in his place.