While Osimhen is still out on his national duty Napoli are going to host Verona in two days. I'm still hoping to see a win of course. The problem so far is that they can't score a lot of goals while conceding quite many. Maybe Verona can also score against them so my expectation is like Napoli to win by 2-1.
After the point loss against Lazio this game is like an opportunity for Napoli to start winning again. But I don't know what they can do against Milan after this game. Especially if Osimhen is still with his national team on that date they can have serious difficulties against Milan.

Actually, it would be quite strange if Napoli couldn't win against Verona later, but yeah, because this season they are a mediocre team so doubts about the results even when facing a team that is weaker than them will still arise.
Verona is very bad in away matches this season, at least they only won once with 2 draws in 11 appearances, so Napoli should be able to maximize this match by getting three points and scoring as many goals as possible, but as you said, Napoli currently seems to be having problems scoring goals, moreover, Osimhen's absence will make their situation even more difficult, even according to statistics, Napoli are much more productive in away matches than at home.
However, my prediction is the same as your prediction that Napoli will win this match even if only by a narrow score otherwise their condition will get worse.
Well Napoli must be able to take advantage of the match against Verona to get 3 points so that they can still maintain their current ranking so as not to fall deeper. Because if Napoli fail to get points in this match then it could be that Napoli will drop further in the rankings.
Napoli have the advantage of being the host so I also think that Napoli will be able to win even with a fairly thin score. But I'll probably still bet on Napoli even though I'm not convinced of Napoli's superiority.