That's true, I expect both team to reinforce during the January transfer window. Also Napoli just got a new manager and before the meeting with Barcelona am sure the team will be executing the new manager game plans very well. That game is going to be an interesting one, it going to be who wants it more that will progress.
Barcelona may not be able to really reinforce their team by getting new players except they have probably gotten over their financial constraints but I think Napoli may be able to do that over the January transfer window this season because they may have the capacity financial as they have not publicly stated if they have any financial challenge recently.
If it were to be last season I doubt if Napoli will struggle to win the current Barcelona who has a weak form currently, but then both teams currently are unstable and inconsistent especially in their various local leagues, but in the UCL so far, they didn't do poorly in their group stage matches so I will not want to judge them completely based on their performance currently in their various domestic leagues as it seems in the UCL the give off a different performance hence it could be possible they will do better in the game than we have expected but it's not going to be an easy one for both teams.