Forget where he might play when both Robin van Persie and Wayne Rooney are fit. For now, we can leave that to David Moyes to sort out.
Because when United issued a one sentence statement on Friday night, they seemed to get some of their aura back.
It had faded slightly over the summer. Sir Alex Ferguson had gone, and a scatter gun approach to the transfer market—very un-United like—ended in a series of humiliating rejections.
But in just 18 words, that was all forgotten:
It signalled a new beginning at United after a disastrous false start in the summer. In the short term, it raises hopes that this season does not yet have to be a considered a complete write-off.
He's just one player, but suddenly, the top four looks achievable again, especially if Rooney and van Persie return from injury sooner rather than later.
But looking further ahead, Mata's arrival means a lot more. And it answers some questions that were threatening to become awkward.
It's proof that United, even without Ferguson, are an attractive prospect. And it shows that Moyes can play the salesman when it comes to signing high-end targets.
Mata didn't have to move to Old Trafford. A World Cup, a European Championship and a Champions League winner about to enter his peak years could have picked his destination.
But he chose United. Even seventh in the league, they are still United. Mata's arrival just reaffirmed it.
It's also a deal that opens up the possibility of other signings. Exciting signings.
And after Moyes unveiled Mata, he said as much, as reported by Stone.
This is the first, and there will be many more to come in time. I want the quality of Juan to be the start of it.
I don't think we will have any more in January. I'm still working on it and looking to do so. But hopefully it will be the first of some new signings, some new players who will arrive, more likely in the summertime.
Rumours that seemed fanciful not that long ago now somehow seem possible. If Mata can choose Old Trafford then why not Marco Reus or Toni Kroos, as reported by the Manchester Evening News?
United will need more than just Mata to turn their fortunes around, but for the first time since the summer, it's easier to believe they are on the right track.