The club announced the deal via Twitter, noting a British record transfer fee of £59.7 million:
While World Cup finalist Di Maria is certainly a player of the calibre that United need to bring in to improve the side—and he will also fit the side's current layout—there are plenty of other problems for Louis van Gaal to sort out which Di Maria will not come close to helping with.
Given the enormous transfer fee, questions will remain over whether United can reasonably expect to improve the team enough this summer to challenge for a top-four place in the Premier League this term.
Di Maria, 3-5-2
United have played out the entirety of pre-season and started each Premier League match so far with a 3-5-2 system under Van Gaal, a system which Di Maria will fit into without problems and add significantly to what United already have on offer for their first XI.
Typically, United will feature a central player who can hold his position in the middle of the pitch, spray the ball around and dictate an impressive tempo, keeping the movement going around him and encouraging others to find space to receive possession.
This will be Ander Herrera, more often than not, with a far more dynamic player alongside him to work hard, pressure opponents in possession in midfield and then break ahead of the midfield line in attack.
That's where Di Maria comes in, as he would offer a far greater threat in the final third than Darren Fletcher can. He's quicker over the ground and does not shirk his defensive responsibilities in the slightest.
Boss Louis van Gaal highlights his abilities, per BBC Sport:
There is no doubting his immense natural talent. He is a tremendously fast and incisive left-footed player who puts fear into the most accomplished defence. His dribbling skills and his ability to take on and beat opponents are a joy to watch. He is an excellent addition to the team.
Simply put, there is no downside to United signing Di Maria for this role, in sporting terms at least. He fits tactically and is a massive step up in quality.
Making the most of that quality relies on other runners and attacking talents, though—but more on that later.
Van Gaal's Winger Wish
The new United boss has spoken previously about United's lack of wingers, which means he is unable, or unlikely, to play a 4-3-3 early on this season. Indeed, per Marca, Di Maria was one of the top-quality wingers that he spoke about lacking.
While Di Maria is best utilised through the central midfield areas, he has proven over several seasons that he can have a significant and consistent impact from the flanks, usually from the right side where he can cut infield on his left foot.
As a scorer and a creator of chances for others, Di Maria is a huge talent who can be relied upon to deliver in the final third. Should United switch within games or over the longer term to playing with two wide forwards, there is no doubt that Di Maria can offer the tactical change option.
BBC Sport's Tim Vickery notes:
Always a dangerous winger, it is in the last couple of seasons that he has become a much more useful all-round footballer. The idea of using Di Maria on the left of a three-man midfield was a bold one, and was not an instant success with the national team. Fast forward to 2014, though, and Di Maria has made progress with the speed of one his forward surges.
Naturally, Di Maria can play the left-sided central midfield role for United's 4-3-3 that he played for Real during the second half of 2013-14.
One Signing Not Enough
We briefly touched upon getting the best out of Di Maria in the middle; that means using his great energy and vision moving up the pitch in possession to link with others, find himself space again and play team-mates in on goal.
While United have a front three—Juan Mata, Wayne Rooney and Robin van Persie—that is the envy of many, the support play from the next line hasn't been up to scratch so far. In part, that has been due to injuries, but United are also badly lacking in either tactical direction or simply genuine quality in the wing-back area.
Ashley Young impressed in pre-season but is not of the standard United require as a regular starter, while Antonio Valencia hasn't managed to impress at all.
In United's system, wing-backs are absolutely key; it's not simply making up ground back and forth down the touchline but serving as a constant out-ball, able to find space, quickly cover long distances and find the playmaking midfield talents infield, stretching the opposition defences across the width of the pitch and delivering quality balls into the box when possible.
Get those players right, and Di Maria's powerful drives forward and ability to exchange passes and positions, particularly down the inside left channel, lift the attacking prowess of the team up several notches. Have sub-standard players in those roles, and they prevent the likes of Mata or Rooney being as effective as they otherwise might be.
Defensively, too, United still harbour plenty of concerns, meaning the midfield quintet (or quartet if Mata is released from such tracking-back duties) have to be more reserved, offer more protection to the back line and thus be less of an outlet to transition play from back to front.
Di Maria is an awesome signing, make no mistake. He was perhaps second only to Luka Modric in La Liga midfielders last season and Real Madrid are going to miss him. However, he alone won't return Manchester United to the top of the English game.
To get the best out of him, they need to improve significantly in other key areas, and there isn't much time left to do so this window.