Mata is a good start on the huge rebuilding job that Moyes faces, however it remains seen whether he can get the best of him. This is a team which has gone from being Champions by 11 points last season to dropping 14 points behind the current leaders in just six months. It tells you that their problems run much deeper, the type that cant be fixed by just one player.
The likes of Liverpool, Spurs and Everton can worry that suddenly United will spring ahead as a result of signing Mata, or you can just see them as a club that just 8 months ago finished a huge 28 points ahead of Liverpool, yet now trail them by 6 points (this is a team that has finished 7th, 6th, 8th and 7th in the last four seasons). This United squad isnt a group of players that need a catalyst to spur them on as Catona and Ozil has done for teams in the past. This is a team that needs a whole new set of players. I see that at least five key members of that squad which will need replaced (Rooney, Evra, Vidic, Ferdinand and Carrick) in the next few windows. Thats not even mentioning the underperforming players in the squad (Nani, Fellani etc), the squad players who are nowhere near good enough in a title winning squad in 2014 (Cleverley, Young etc). Thats not even mentioning on how he goes about replacing the likes of Giggs and Scholes within the squad.
There is no question on whether Mata will be a success at United, he will but I dont think one signing stops the slide. Look at Liverpool signing Suarez and look how long it has taken us to compete for the top four. It takes some time for players signed in previous years to look settled and a few windows to really start to push on again. Why are United any different?
Short-term, however I see them picking up a lot of points if Mata hits the ground running. Out of the big seven teams, they have two away games and not to mention their impressive away record this season against the dross at the bottom half of the table. That's not even mentioning Rooney and RVP coming back soon.