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Sergio Ramos is the most successful centre-half Manchester United have been linked with this summer. Mats Hummels has been repeatedly linked with United, per Marcus Christenson of the Guardian, for example, who reported in May that the German had turned down a move to Manchester.

Hummels has a World Cup and a couple of Bundesliga titles to his name—a respectable haul indeed.

Ramos, though, is part of the group of Spanish players who dominated the international scene for half a decade, winning back-to-back European Championships in 2008 and 2012 and the 2010 World Cup—the country's first.

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He has not done too badly on the trophy front at Real Madrid, either, though Barcelona's dominance has kept his tally down more than he would have liked. Three Liga titles is probably fewer than he would have expected to win when he signed for Real Madrid from Sevilla in 2005.

To those he can add two Copa del Rey titles and the 2013/14 Champions League—the precious Decima that Real chased for so long.

He has been at the top for a long time. A significant portion of his career has been spent at right-back—indeed, that is where he started both the Euro 2008 and 2010 World Cup finals. Since the latter, though, he has made the permanent switch to centre-half.

Playing alongside Pepe at Real Madrid, he has been part of a partnership gifted in football's dark arts, as well as just plain gifted.

The first thing he would bring to United, then, is bags and bags of elite-level experience.

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It would be an expensive transfer, with Rob Draper of MailOnline reporting Ramos would be earning £260,000 per week at United, an astronomical amount for a centre-half.

James Robson of the Manchester Evening News cites "sources in Spain" as reporting the "deal will be worth around £53 million, including [David de Gea]." Exactly what that equates to in financial terms depends on the two clubs' valuations of De Gea.

This would be huge money for a player with the prime of his career in front of him and some potential resale value down the line. For 29-year-old Ramos, it is a fortune.

However, it may well end up representing value for United. The current need is not for a player with potential who could be sold on somewhere down the line. What the current back four needs more than anything is an experienced leader in its midst.

In Chris Smalling, Phil Jones and even Paddy McNair, there is plenty of potential. Smalling and Jones have plenty of football under their belts, but neither has anything close to the experience of leading a back line that Ramos has.

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In terms of his disciplinary record, Ramos' leadership comes at a cost. In March 2014, he broke Real Madrid's all-time record for red cards, as covered by Louis Richards in the Guardian at the time.

However, the good has certainly outweighed the bad. Appearing on talkSPORT, former Liverpool defender and Sky Sports pundit Jamie Carragher defended Ramos after some United fans called in to express their displeasure at the link (h/t Sky Sports):

I get a bit wound up by the criticism Ramos gets. This is a fella who has won everything, he plays for one of the best clubs in the world and one of the best international sides we’ve ever seen. He is rash at times, he has moments of madness and does get overly emotional in games, that’s always been a problem for him, but let’s not forget that it’s a problem for Wayne Rooney as well.

Ramos is still the most frequent fouler in the Madrid side—he averaged 1.6 fouls per game in La Liga in 2014/15. That would not have got him top of Manchester United's fouls league, though—he would have had to settle for second behind Marouane Fellaini's 2.3 fouls per league game.

In truth, United's back line could use an addition of sensible aggression. While Ramos walks the line—and frequently oversteps it by some distance—there is a place in a defensive setup for someone who is prepared to make his presence felt with strikers. Centre-forwards facing Ramos know they are in for a battle.

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Ahead of the 2013 clash between Madrid and United, Ramos was interviewed by Sid Lowe of the Guardian. He said of his upcoming battle with Wayne Rooney: "He's hard-work, heavy going. He enjoys the physical challenge. I prefer that, to be honest. I like that defender versus striker battle, that challenge."

What he said next, though, shows that he is hardly just a thuggish hard man:

Rooney's mobility is difficult: you don't always know how far to step out to pressure him. He drops deeper, or pulls wide and you wonder whether to follow. The communication with the midfield is vital. If he drops, there's a point at which the centre-back can't follow him and the responsibility passes to the midfielders. Go too far and you leave space behind.

This simple explanation of the challenges of facing a forward such as Rooney shows Ramos as a player who thinks about the game. It is easy to imagine Louis van Gaal reading the above and nodding approvingly. That kind of positional intelligence is why Ramos also leads the Madrid squad for interceptions per league game.

He is also very quick, as this tweet from Bleacher Report's Will Tidey indicates.

Leadership, physicality, a willingness to bend the rules in his team's favour, pace and an excellent understanding of the game—these are all qualities Ramos would bring to United, and they are all qualities United need.

There would be some adjustment to the Premier League required. However, it could suit Ramos' game to play in a league that tends to allow more physical contact.

While he may sometimes be too hot-headed for his own good, he has also demonstrated a phenomenal capacity for coolness under pressure.

In the semi-finals of Euro 2012, Spain needed a penalty shootout to get past Portugal. Ramos had missed the decisive penalty in Madrid's Champions League semi-final shootout defeat to Bayern Munich a few months earlier. He did not shirk responsibility, though. Instead, he found it somewhere inside himself to successfully attempt a Panenka for his country.

It was the kind of moment a player with Ramos' X-factor is capable of producing. It is the kind of hard-to-quantify-but-you-know-it-when-you-see-it moment that only first-class players can produce.

Special moments seem remarkable in isolation. However, such moments are in fact built on years at the top in the mindset of a sportsperson who knows their own abilities and can trust themselves to execute.

It's worth remembering that the talk at the moment is just that. United fans watch transfer rumours wearily, as links with their club are seemingly often used to ensure a more favourable contract with the player in question's current employers.

However, according to Lowe, writing in the Guardian on Monday: "Ramos believes Madrid have repeatedly briefed against him in an attempt to damage his reputation and his standing with supporters, portraying him as a money-grabber not interested in the club."

If it turns out that this is not all posturing and United to somehow manage to bring Ramos on board, their chances of winning next season's Premier League should considerably increase. That is what he could bring to the club and why this is a signing that would be genuinely exciting should it come to pass.

All advanced statistics per WhoScored.com.