Even though so far Napoli has appear quite tough in Serie A, what needs to be considered is that the teams play in the Champions League are the best teams represent their each league. This of course will be very different from Serie A, Napoli will meet the opponent who have never before they found in Serie A
And I think Napoli are quite lucky because in the round of 16 they will play Frankfurt, not another favorite team and this is enough to open their chances of getting to the quarter-finals, it's just that they have to maintain good performance because by continuing to advance in the champions league will make them have quite a lot of matches to live without being able to maintain performance will make them lose both.
Talking about Eintracht Frankfurt, I also think that they cannot be underestimated at all at this moment, because even Eintracht Frankfurt last season managed to get rid of Barcelona in the Europa League. Also, Eintracht Frankfurt started this season in the Bundesliga not so well, but as time goes by Eintracht Frankfurt can get into the top four in the Bundesliga and at least that proves that Eintracht Frankfurt really can't be underestimated this season.
Napoli and Eintracht Frankfurt at this moment are teams that are experiencing an impressive increase in performance, so that any results in this match can still happen.
I mean, even though Napoli is an unbeaten team in Serie A, that still can't guarantee that Napoli will get the convenience to go further in this Champions League.
Therefore, I personally still can't say that Napoli will win. Also, whether or not they have changed after the break, I'm still pretty sure that Eintracht Frankfurt will still provide strong resistance in this match, which means that Napoli and Eintracht Frankfurt will never be easy to get a win at this stage.