Don't underestimate Franfrurt, they managed to win against Bayern Munich. Napoli at this time are indeed in a good state, their record in the league is amazing. One loss in twenty-three matches. But they will play in Germany and I think Frankfurt remain favourites to win.
I don't see how these two teams play in their respective leagues, even though Napoli are better quality than Frankfurt, but the problem is that Frankfurt is playing at home so they are more in the favorites for the first leg. Napoli can play it safe if they want to qualify for the next round, holding Frankfurt to a draw away from home will be a good capital for them when they have the second leg at the Diego Armando Maradona stadium.
Another match I'm waiting for is Liverpool vs Real Madrid. Liverpool are unstable in the League and Madrid are the same, they lost a few points in the league. Tomorrow's Liverpool Vs Real Madrid match will probably end in a draw.
Both of these teams have shown good results in the previous two matches in their respective leagues, but in general Real Madrid has more chances to bring full points from Anfield, considering that Real Madrid's consistency in the Champions League is more reliable than Liverpool. My prediction is Real Madrid will win this game with a small score and I don't think the match will end in a draw.