There was a moment towards the end of Chelsea's victory over Manchester United when it seemed that Jose Mourinho was toying with Juan Mata. As the clock ticked down he summoned the Spaniard to warm up in preparation for the Blues' final substitution. Mata duly obliged, despite his obvious frustration at the small offering of a late cameo, but returned to his seat only to find that Nemanja Matic was being sent on instead. Chelsea ended the game with four defensive midfielders on the pitch while Mata remained an unused substitute for the third match in a row.
Much has been said about the playmaker's strained relationship with Mourinho, resulting from the manager's intention to develop Chelsea's style following Rafa Benitez's brief reign. At first it seemed preposterous that the Portuguese could leave out a player who had recorded the highest number of assists in the last two Premier League seasons, but over the last five months his decision has been vindicated. Mourinho is renowned for being meticulous in his approach and his meagre use of Mata isn't driven by any personal agenda.
That hasn't prevented speculation. At the start of the season there were many columns written in support of Mata, questioning Mourinho's iron fist that also excluded Iker Casillas in his final year at Real Madrid. But Casillas has not made a single appearance in La Liga under Carlo Ancelotti, and nor has Mata taken his chances to reaffirm his quality. His last appearance, in the 3-0 win at Southampton, was cut short on 53 minutes with Chelsea drawing 0-0. The playmaker's exasperated reaction to his substitution again raised questions over Mourinho's man-management, but it was easy to dismiss any doubts.
"The plan worked," said Mourinho. "Sometimes it doesn't, sometimes it does. This match was difficult. You need to work a lot to play against Southampton. Willian and Oscar gave a different intensity and we finished the game in a comfortable way.
"I think his frustration was that we had to win and when he came off, the team was losing two points. At the end everyone was happy in the dressing room so I have to believe that."
That Mata hasn't featured since he was replaced at St Mary's has afforded Mourinho the perfect conclusion to the debate and renewed speculation that he could depart Chelsea mid-way through their first convincing title challenge in three years. Had he been the Blues' most important player in a period of sustainable success then his sacrifice would seem absurd. But Chelsea have been a long way behind Manchester United and Manchester City since sacking Ancelotti in 2011. Their Champions League victory in 2012 indicated as much as anything that Mourinho's plan to build a long-term playing model was necessary.
The same is clearly true at United, with whom Mata has been linked in a potential £40m transfer. David Moyes needs a marquee signing for several reasons; firstly to aid the immediate pursuit of a Champions League place, but also to banish the lingering suspicion that the champions are no longer an attractive proposition now he has replaced Sir Alex Ferguson. However, Mourinho's perceived lack of faith in Mata should be taken as both an opportunity and a warning.
When Gary Neville spoke of Mata being the antithesis of United's 'philosophy' on Monday, he may have had a point. "They would have to change to accommodate Juan Mata in the way they normally play," said Neville. "They normally play with wide players. Sometimes they tuck in, but generally they have wide players and the thing for me is where is he going to play? What it could be is the start of something to lead to other things, but typically I wouldn't say he fits."
Although he spoke of philosophy, Neville was referring more directly to United's style of play which, at its finest, has always centred on quick counter-attacking with pace down the wings. But it is in this respect that Mata is lacking. There are few players quicker in speed of thought, with the Spaniard capable of picking even the most robust locks, but his attributes as a No.10 do not lend themselves to the identity that Ferguson created at United, or the reliance on width adopted by Moyes.
It is arguably a lack of pace that has seen Mata marginalised by Mourinho. The manager spoke of needing a "different intensity" against Southampton and Eden Hazard, Oscar and Willian all use their speed both to counter-attack and press their opponents into mistakes. Mata has shown that he can adapt to different systems during his first two years at Stamford Bridge, but becoming quicker is not a realisable aim.
This is not to say that he wouldn't succeed at United, and his many talents deserve appreciation. As the jewel in the crown at Old Trafford, it is easy to imagine the 25-year-old thriving again, but suggestions that he can be a quick fix are fanciful. The biggest concern over Moyes thus far is his failure to develop a convincing playing style. While Mourinho has achieved that by sacrificing Mata to steer Chelsea two points behind Arsenal, Moyes must ensure that he knows exactly how to use the playmaker if he is to transform United's fortunes. If Mata does sign for the champions, he will be the first brick in building a new ethos ahead of the widely anticipated changes in the summer. As Neville said, it would be the start of a new approach, not the finishing touch to a plan already in existence.
Matt Stanger - he's on the Twitter.
Yes all very good Matt, but it's Juan MATA....he who was Chelsea's player of the year two years in a row. Has a lovely beard....Better than Tom Cleverley....Juan MATA!- mufc phil