Barcelona aren't having the best of times in La Liga at the moment, but they finished top of their group in the Champions League with 12 points. They had tougher opponents like Shakhtar and Porto. Napoli only had Real Madrid. A dead Union Berlin and almost the same Braga. I think Barcelona have a better chance than Napoli.
I also think that the chances of winning the match are for Barcelona, but we also have to see how the Napoli team develops in January because their match will take place in February which means each team can make changes for the better before welcoming their important match in in February next year. Although if you look at their current level of strength, it is a little more convincing for Barcelona to win this match even though Napoli is the home team in that match.
With the time available, we must also wait to see if they will experience a change in their performance, be it for the better or for the worse. Both will have their fate in their own hands during the preparation period. Barcelona and Napoli are in a bad situation now, especially for Napoli, they are very diferent from the Napoli I saw last season. Although last season they also had to be eliminated by a club from Serie A as well but at least they had a more believable performance at that time.
Now they have weaknesses at some point, as well as Barcelona. Both coaches will have to prepare these teams well before they meet next year.