I don't think the match against Napoli is actually going to be easy for Barcelona to be honest. Barcelona has been facing a good amount of problems this season. Napoli also has not been the best of teams lately but the thing is Barcelona also has a lot of injury problems as well. Actually, both of them are going through the same kind of problems, to be honest now that I think about it. Both of them have to defend the league title and both also have to do very well in the Champions League as well. And both have the same kind of problems except for the fact that Barca has a few injuries. Barca is falling off in the La Liga pretty badly, to be honest. So I also think Barcelona might think about giving the La Liga a better chance instead of the UCL. Anyway, I think the match against Napoli is going to be competitive.
Barcelona has inconsistent performance on last several matches group phase although qualify as first standings position place, against Napoli on 16 round is not easy for them after poor performance not only in Champion League but also in La Liga. Napoli have difference level performance when playing in domestic league or Champion League although their performance not quit well in Serie A seems they will try to get higher round in Champion League by defeating Barcelona.
Barcelona faced problem with key players have injury, although winter transfer window opening few days later less financial support from management Xavi Hernandez difficult find replacement for some position with his players injury.