The biggest problem I see in Matheus, is that he plays like a floating flower..
Let's say second ball situation, 50-50% chance to win it and you have to engage in a physical duel with the opponent.
In those scenarios, Matheus for me seems like a guy, who always looses.
Nothing is greater than a player, who holds the fucking ball and wins it as well.
That's the first thing I would work on him to improve and I don't think that's something that couldn't be improved. I don't know GYM maybe, some special training sessions where you work on stuff like that and get stronger, tougher.
If he gains that skill and we add his great technical abilities to it, then we have a decent player..
In short, he needs to grow some balls :D