I have three problems with Jose's idea concerning Mata as a winger
1) Mata has changed a lot since his Valencia days. He's no longer a winger. His mentality is that of a #10 now. Put him on the wing and he'll still drift to the middle to play the way he likes to play (puppet master of the final 3rd of the pitch). If Mata ends up drifting towards the middle, then he's not providing width (which is one of Chelsea's main problems atm).
If Jose wants to convert Mata back to a winger again and get him to provide width, that's not a great idea. Mata's not as quick as he used to be and is not as fast as the other wingers in your squad. So what use is Mata as winger during counter attacks? And Mata hasn't got the pace to dribble past multiple players when cutting inside like Robben can. So it makes Mata's job harder if he's played as a RW. Even if he plays LW, his lack of pace will still be a problem when it comes to getting past players.
2) It's clear that one of Jose's biggest problem with Mata is his poor defensive ability/not tracking back and getting stuck in. Well, if Mata is such a defensive liability, why not play him in the #10 role where he doesn't have to do too much tracking back and just play someone else on the wing instead? Surely that makes more sense logically than playing Mata on the wing where he'll be more of a defensive liability?
Even worse is that Mata hasn't got the biggest lungs in the world. I don't think he is fit enough to bomb up and down the wings to attack and defend all game. It doesn't make sense that Jose would want someone like Mata, who isn't the fittest player around, to be tracking back to defend all game.
And while Mata can improve defensively in the #10 position, it's hardly the most important position to defend from. And it's not that hard for Jose to coach Mata to do a better job defending from the front, is it? It's not like Mata has to be Baresi-esque when defending from the front, does he?
And anyone remember the Spurs 2-4 Chelsea game last season? Remember when Mata pressed Walker and made him fall over, then went on to set up Sturridge for the 4th goal iirc? How awful from Mata, eh?
3) Lastly, Mourinho has clearly stated he thinks Oscar is better at #10 than Mata. Now, I'm willing to admit that opinions can be subjective. But when Mata has been your player of the year for two seasons, I think it's fair to say that Jose is talking BS about Oscar being a better #10. Yes, Oscar might be playing well. But it's not about the individual. It's about the team. Mata provides better creativity in the #10 role and so far, he has been better at pulling the strings in the final 3rd of the pitch than Oscar.
Jose can keep talking about changing the philosophy of the club blah blah blah. But if he truly is on the same page as most fans about playing attractive but equally effective football, then Mata has to play #10. All Jose has to do is coach him to be better at defending from the front even though he won't be as good as Oscar at doing it. Let the other midfielders and wingers do the major defending.
1) It's either Jose is being a prick deliberately to throw his weight around the dressing room.
2) He genuinely thinks Oscar is better than Mata in #10 in the system that he envisions for Chelsea.
3) He hates Spain after his time managing Madrid. So he's treating the Spanish players in Chelsea like pieces of ****. Hence why Azpilicueta hasn't got a game yet to try and prove himself (however Ivanovic has generally played well so far).
We should all give Jose a chance to prove himself. But even if Chelsea get good results with Mata not playing as #10, I will still disagree with Jose on this matter. I will always believe that Chelsea can get even better results and performances with Mata as #10.
My 2 (rather long) cents.