The Napoli we saw last season can comfortably beat the current Barcelona team, but it's quite unfortunate that the Napoli we are seeing now are just a Shadow of the last season team. This match is going to be keenly contested. Both Barcelona and Napoli are not doing very well in their respective leagues. Both Napoli and Barcelona can advance to the next round so it will be difficult to determine who will qualify.
The Napoli vs Barcelona match is still quite far away and both of them still have time to improve their performance in January because both of them can take advantage of this time to change all their current shortcomings for the better. Because in general these two teams are not doing well right now so they have to make a lot of improvements in each line of players in order to recover from the bad performance they have experienced so far.
I don't know what will happen in their squad or in their form in that long time, anything can happen. But it's going to be a tough game for both of them because in the domestic league they're not doing too well either. Although Barcelona managed to win the group, the group they were in was an easy group because it was inhabited by several clubs that were not better than them. Napoli are also the same, they became runnersup, but the 2 clubs that did not qualify were not superior clubs so they could also be easier to advance to the next round.
Barcelona and Napoli have a long preparation time and I hope they can make good use of it. They can also take advantage of the transfer market to add to their ammunition.