Brendan Rodgers' Foxes are top of Group C but still have work to do to progress to the knockout phase.
Leicester, who beat Legia Warsaw 3-1 last time out, lead Spartak Moscow and Napoli by one point ahead of the final gameweek.
A win in Naples will see them through as group winners.
But they will exit the tournament should they lose and Spartak beat Legia in the other tie.
Napoli v Leicester: talkSPORT commentary
The Europa League clash is set to take place on Thursday, December 9 and will kick-off at 5:45pm UK time.
Coverage will start from 5pm with Alex Crook and former Tottenham and Manchester City striker Clive Allen.
Napoli v Leicester: Team news
Leicester will be without seven players through illness for their trip top in Italy.
Rodgers confirmed some of the unnamed players had tested positive for coronavirus, while others had been left at home as a precaution as they felt unwell.
Three members of the backroom staff have also not made the trip.
"We have had some positive cases and some people who are not well so we haven't taken the risk," Rodgers said.
"We will have seven unavailable. It's been the last few days really, you're starting to see a few more cases. It's about the health of our players and we have to respect the travel, coming into Italy.
"We still have a strong squad here, but unfortunately not a fully-fit squad."
Youri Tielemans is back in contention after a five-game injury lay-off and left-back Ryan Bertrand is also available.
Napoli v Leicester: What has been said?
Napoli boss Luciano Spalletti: "All matches are important and decisive, but we didn't treat them that way, that's why we are in this situation right now.
"The difference is that this one is a really decisive one.
"These are the matches that show the strength of the player. This is a match where there is no second chance. It is decisive."
Leicester boss Brendan Rodgers: "It's one we're very comfortable in, knowing the fate is in our hands. If we win, we top the group, if we don't lose, we qualify.
"The key is to be positive in our mindset and try to win the game. It's what we look to do. We had a really good performance against Napoli at home. They are an excellent team, but the team has a confidence there."