Napoli are performing very poorly in the Italian league which is why they must focus more on Serie A even though they are already far behind. Inter, Juventus and Milan are many points ahead of them. So it will be quite difficult for them to bridge this point gap and hope to be in a good position again. But since they have a record of doing well in the past, they can come back to a good position if they try. So they should pay more attention to their performance
The draw back of Napoli currently, I think it's just a temporary one and they will definitely get over it especially if they don't suffer injuries again or been limited by internal crisis around the team. They were the winners last season, they recently changed their coach so I think it's a little set back they will be going through for awhile.
After awhile when they must have totally gotten used to their new Coach I'm sure they will be doing much better but I doubt if they will be able to defend their title this season because their performance isn't as good as it was last season. Juventus and inter Milan are definitely the most liable to win the title this season, especially inter Milan who has performed really well this season and Juventus aswell has been been at their best too and have been at the top a few times this season, it's mostly between Juventus and inter Milan to win the trophy this season.