Back when Pep Guardiola and Alexis Sanchez were at Barcelona, the manager and his backroom staff used to regularly get frustrated with the Chilean, because he would so frequently break a core principle of the club. And this was nothing to do with discipline or dressing-room relations.

It was that when Sanchez got the ball for Barca, he would immediately put his head down and burrow forward in that single-minded way he does. Guardiola and his staff however would expect that every single Barca player get the ball and look up, look where their options where, and display some ‘pausa’.

This issue was one reason why many were surprised when the Manchester City manager so intently went back in for Sanchez over the last year, but also touch on why there is so much more to the player’s decision than money. There are a few angles to the big question as to what club the Chilean should choose, not least the angle of the shadow cast by a club as massive as Manchester United.

Manchester United's January transfer targets Show all 7 1 /7 Manchester United's January transfer targets Manchester United's January transfer targets Fred Club: Shakhtar Donetsk

Likelihood: 5/10

Manchester United's January transfer targets Lucas Moura Club: Paris Saint-Germain

Likelihood: 3/10

Getty Manchester United's January transfer targets Danny Rose Club: Tottenham Hotspur

Likelihood: 2/10

Getty Manchester United's January transfer targets Alex Sandro Club: Juventus

Likelihood: 2/10

Getty Manchester United's January transfer targets Malcolm Club: Bordeaux

Likelihood: 2/10

Manchester United's January transfer targets Ryan Sessegnon Club: Fulham

Likelihood: 2/10

Getty Manchester United's January transfer targets Kieran Tierney Club: Celtic

Likelihood: 3/10

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It should not be naively overlooked that money is still a big part of this of course. Those who know Sanchez – and there are not too many in football that really know a prickly character that well – say it is a big factor for him, and he wants to get the best deal possible.

United are willing to offer that, ultimately to greatly trump the length of time that Guardiola and City have spent putting into this deal. That is the short of it. There is a long, too.

It would be similarly naive – or just blinkered – to deny that City are probably the most propitious choice for a top professional right now, maybe in the whole football world, as Rio Ferdinand argued on BT Sport on Saturday night.

They have the medium-term excitement around a manager who is probably the best in the world right now in Guardiola. They have the long-term expectation from what is the lavishly-funded and likely most forward-thinking infrastructure in the world, too. Finally, they have the short-term promise of an almost guaranteed Premier League medal, and maybe even a quadruple.

Sanchez would essentially be giving up what would be just the fifth title of his career, and only the second outside South America, if he chooses United.

That’s how far City are ahead, and it is interesting how recent history has been inverted, how it looks like it is now United who have to use base finance rather than pure football to convince a player.

But it’s not quite that simple, or binary.

Pep Guardiola and Alexis Sanchez have history - and not all of it good (Getty)

Mourinho is one of the most persuasive coaches in the game when he can get to speak to a player, such is his mastery of sports psychology, and – like Sir Alex Ferguson used to – will have talked up how strong United can be with Sanchez.

That should not be discounted as mere words, or designs for next season. There is still a lot to play for this season.

As far ahead as City are in the league, and as exceptional as they look, there are no such guarantees in the Champions League.

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A bit of tactical acumen, a bit of luck, and a bit of sparkle can still go a long way in a knock-out competition like it, and undo even the most intensely brilliant side on any given night. United have much more than that.

For all the criticisms of Mourinho’s fundamental football outlook in the modern game, his reactive approach is still very suited to knock-out football, and would only be amplified by a proactive attacker like Sanchez. The manager’s forensic mindset and defensive stability combined with the pure attacking thrust of the Chilean could be quite a force. It could deliver the Champions League.

This is also one area where all of the debate about Mourinho’s approach compared to Guardiola’s could actually be inverted, too, and where that tunnel-minded individualism Sanchez displayed at Barcelona could be key.

Mourinho's ability to talk players into moves should not be disregarded (Getty)

For the vast majority of attackers in the world, it should be a no-brainer to work with a coach like Guardiola to bring on your game; to take those edges and make you a purer player. It is those edges, however, that make Sanchez the raw aggressive force that he is; a difference-maker. It points to a big difference in his choices.

How often would we see situations at City where the Chilean tries something, but it frustrates Guardiola, because the extent of his individualism undoes the orchestrated work of the team? That is worth considering.

Given the Catalan had wanted Sanchez so much, he had obviously considered this, too. It could even be argued that the one thing missing from City’s wondrously slick game is a bit of brute force. They could maybe do with that defiant street-fighting when something different is called for, a knife to be taken from the teeth to just cut a team when they can't unravel them.

Sanchez has won just one league title outside of South America (Getty)

It isn’t a stretch, however, to believe it is one reason why City are suddenly not absolutely intent on the player and why Sanchez is having second thoughts beyond money. Guardiola moreover wants players fully ready to buy into his philosophy, and if money diverts someone from that then it is just one other reason – at least according to those close to the Catalan – why he would be willing to walk away.

Mourinho’s more laissez-faire approach to attackers would not just allow this individualism, but maybe prove most beneficial for both team and player. One of the issues with the Portuguese’s approach is that when his sides are not on form, there is no system to fall back on, and they become predictable and uninspired. Sanchez is anything but predictable, however, and maybe the most persistent and relentless attacker in the modern game.

Sanchez would remain the undisputed main man if he joined United (Getty)

This throws up a final angle. Sanchez is famously a player who never wants to rest, who is never happier than when he just has a ball in front of him, and it has even led to Arsene Wenger having to contain him to prevent him going into the “red zone” as regards injuries.

At City, however, he would just be a fine attacker amid a range of them, more regularly rotated. At United, he would be the undisputed main man, always playing.