From pundits to players, managers to club legends, everybody's said their piece about Chelsea's decision to sell Juan Mata to Manchester United for a club record £37million fee.

Arsene Wenger and Manuel Pellegrini have both condemned the move, the former suggesting the January window should be abolished in its entirety and the latter arguing for a re-writing of the transfer rule-book.

The Arsenal and Manchester City bosses would like to think their criticisms are directed towards the make-up of the mid-season transfer window rather than the Mata case itself, but deep down, both are clearly infuriated by Jose Mourinho electing to strengthen a club that's dominated the Premier League since its incarnation during their lowest low for the best part of three decades.

Why would the Chelsea gaffer willingly hand over one of the division's most potent attacking midfielders to a Manchester United side on its knees and begging for mercy? Surely in the long-run, refusing to strengthen the Premier League champions would have not only benefited the Blues, but the rest of the top flight.

Financial Fair Play, Mata's personal ambitions for the 2014 World Cup, and the fact Manchester United have taken on Chelsea twice already this season but are still yet to face City, Arsenal and Liverpool, undoubtedly factored into Mourinho's decision to let the Spain international join one of the Blues' closest divisional rivals.

But are we overlooking the psychological impact Mata's move will have on both the United and Chelsea camps as the most subliminal yet decisive cause?

The Daily Mail's Martin Samuel touched on the issue slightly, when he lead with the headline last month 'By selling Mata, Chelsea are saying United are a spent force'. Considering the Blues' 3-1 triumph over the Red Devils, coming days before the Spaniard's departure, was essentially the final nail in the coffin of United's Premier League title defence, I'd certainly subscribe to that theory.

But there's more to it than that. The modern transfer market requires an overseeing eye that can plan for three or four seasons in advance, and Mourinho did not hand over a two-time Chelsea Player of the Year simply to reinforce what we already know about United's current campaign.

Let's remember that Mata represents the first player to switch allegiances between both clubs since Juan Sebastian Veron almost a decade ago, moving the other way for £15million in 2004. That year holds great significance as the last transfer interaction between the two sides, just a season prior to Chelsea claiming club to back-to-back champions under Jose Mourinho, fuelled by the finances of Roman Abramovich.

Since then, dealings between Manchester United and Chelsea have been a no-go, as both sides continually battle year upon year for the English crown. In that time period, Manchester United have let players leave for Manchester City, and Arsenal have sold to pretty much everyone, but the Blues have always refused to sell to divisional rivals. Even Demba Ba's loan move to the Gunners was blocked by the club's management in the summer, despite Mourinho issuing the striker just two Premier League starts since.

This is what makes the Mata transfer saga so special, not only because of its rarity, but because of the timing.

This did not come in the summer when Manchester United were still an unknown quantity under David Moyes, despite Jose Mourinho being firmly in the knowledge even back then that the Spaniard would not feature heavily in his plans, with Oscar anointed as Chelsea's new golden boy in attacking midfield.

Rather, the transfer materialised after Manchester United had gone an entire half-season without once making it into the Premier League's top five, and after Juan Mata had spent six months on the Chelsea bench, with his appearances amounting to just 834 minutes worth of top flight football.

By selling Mata to United, Mourinho is saying; "Look at you, Manchester United, once so strong. A club that has won the Premier League title 13 times out of a possible 21 attempts. A club who walked away with the title last year in an almost mechanically destructive fashion. You now come, cap in hand, to a club that hasn't won the title in three years, requesting the services of a player who I don't even want in my starting XI to be your saviour".

That is the psychological benefits of Chelsea's decision to sell in a nutshell; Manchester United are at such a loss, they've paid a club record fee for a player who wasn't even guaranteed a regular spot on the Blues bench. It's not suggesting United are a spent force, and therefore there is no risk in selling them an attacking midfielder that claimed twelve goals and twelve assists in the Premier League last season. It's illustrating the desperation of one club, compared to the confidence of another.

Some would even argue Chelsea have sold Manchester United a player they don't need, and their recent downfall has clouded their transfer judgement. While Wayne Rooney remains at the club, David Moyes will always struggle to fit Mata, the England international and Robin van Persie in the same starting line-up without compromising each individual's ultimate utility.

Jose Mourinho has been labelled a master psychologist before, but this could be his greatest victory in the battle of the mind games yet. To many at Old Trafford, Juan Mata will be a poster boy of hope and optimism, a cause to look beyond the current campaign. But to the rest of the Premier League, he will be an eternal beacon of how the mighty have fallen, a reminder of Manchester United's lowest low and David Moyes' flustering desperation.

And as long as that subliminal narrative remains, Mourinho will always feel he and his Chelsea side have the psychological upper hand, for he was the man Manchester United were forced to turn to when they needed a savour. It's a simple case of 'remember who your daddy is'.

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