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.