Winning big teams in pre-season does not mean that the club is strong and that Fonseca has worked on the team performance because in such matches most coaches don't take the match serious because it is only an experimental match and nothing more.
I do say it often that your performance in the main league is what matters and not your performance in friendly matches. A lot of big teams that lost their pre-season matches are so winning now in the main league because this is what counts.
Fonseca hasn't managed any big teams so far, and because of that he might be having some hard time with Milan as well. I said the same thing about Kompany at Bayern Munich recently, and because of that I think it's quite important to remember that we are going to end up with much bigger results if we are not careful and the loss could be huge because these are managers that may have experience in general, but not experience at a club this big.
Milan is the biggest team he has ever managed, and because of that he is having some hard time getting adjusted to something this big, if Milan wants quick success then they should hire someone that comes from a big club already.
There aren't really that many of them available at the moment, but Xavi comes to mind and he was available and they didn't want to because usually non-Italian managers at Italy do not do that well. Which is why I think it is going to end up with some time consuming situation and they need to wait for it. If they can wait for it then they are going to get a good result. Most people will not be happy with what they have at the moment, but they do have something good and they shouldn't really be worried about it.