Meanwhile, their hosts sit second in the section with six points to their name and could move within touching distance of a place in the knockout rounds with another positive result.
Match preview
With managerial uncertainty, lacklustre displays on the field and bizarre TikTok scandals rearing their ugly heads, life at Napoli has been far from flawless for Rudi Garcia, but the reigning Serie A champions appear to be turning a corner if recent results are anything to go by.
Since suffering back-to-back losses to Real Madrid and Fiorentina at the start of October, Napoli have three wins and a draw on their record from their last four matches continentally and domestically, including a 1-0 beating of Union Berlin two weeks ago thanks to a solitary Giacomo Raspadori goal.
The manner of that victory was far from convincing, though, as the German upstarts squandered numerous chances to breach the Partenopei backline, but only five days later, Garcia's side gained one point while AC Milan lost two, recovering from a 2-0 deficit to hold the Rossoneri to a 2-2 Serie A stalemate.
Raspadori was on target once again - as was Eljif Elmas - when Napoli's visit to Salernitana on Saturday ended with Garcia's men running out 2-0 victors, and should Napoli get the job done versus Union Berlin this week, they will move to within a point of a last-16 place if Real Madrid put Braga to the sword.
If the hosts are to enjoy another deep run in Europe's premier tournament, a measly record attacking record in their first match against Union Berlin - comprising six shots and 0.25 expected goals - cannot be repeated, but Napoli have never suffered back-to-back home losses in the Champions League.
On any other day, Union Berlin could have emerged from their meeting with the hitherto imperious Italian champions triumphant, but Urs Fischer and co still possess that unwanted losing feeling as things continue to go from bad to worse for this week's visitors.
Starting as they mean to go on in August with a trio of consecutive wins - scoring 12 goals along the way - Union Berlin are now living a nightmare, losing a staggering 12 matches on the bounce across all competitions and failing to find the back of the net in each of their last five encounters.
The Iron Ones' defence was carved open at will by Eintracht Frankfurt in a 3-0 Bundesliga beating over the weekend, leaving the Champions League participants in the relegation playoff spot after 10 matches, and they are one of only three teams without a point on the board in the 2023-24 Champions League - Benfica and Royal Antwerp are the other unfortunate souls.
Not even a draw on Wednesday would be enough to keep Union Berlin fighting another day in the Champions League, although Fischer's side gave a good account of themselves in their first European away game of the season, only succumbing to an injury-time Jude Bellingham goal in a 1-0 loss to Real Madrid.
Valiant displays that do not put points on the board are meaningless to Fischer's troops, though, and barring the start of an unforeseen revival in Naples, Union Berlin's maiden Champions League journey will come to a premature end.
Napoli Champions League form:
W
L
W
Napoli form (all competitions):
L
L
W
W
D
W
Union Berlin Champions League form:
L
L
L
Union Berlin form (all competitions):
L
L
L
L
L
L
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Team News
Once again, Napoli should only be working with a solitary injury concern for Wednesday's game, although it is a significant one, as Capocannoniere winner Victor Osimhen is on the road to recovery from a hamstring issue and should not return just yet.
In his place, hotshot Raspadori will aim to make the net bulge for the fourth game running as he joins Matteo Politano and Khvicha Kvaratskhelia in the final third, but Elmas's goal should not be enough for the North Macedonia midfielder to force his way in.
Further back, Brazilian defender Natan is back from a one-game domestic suspension and is in line for a third successive Champions League start, most likely in place of Leo Ostigard.
As for Union Berlin, the Iron Ones' crisis reached a new low last month when on-loan Chelsea forward David Datro Fofana - who caused Napoli a world of problems at the Olympiastadion - was briefly suspended after refusing to shake his manager's hand after that loss.
Burned bridges have since been rebuilt, though, as Fofana completed the full 90 against Frankfurt, while Alexander Schwolow (hip), Andras Schafer (foot), Danilho Doekhi (knock) and Josip Juranovic (muscle) missed that game, but the latter could return on Wednesday.
Midfielder Rani Khedira is also primed to provide some fresh legs in the engine room amid his three-game domestic suspension, and a recognisable XI should be fielded despite the visitors' current predicament.
Napoli possible starting lineup:
Meret; Di Lorenzo, Natan, Rrahmani, Rui; Zielinski, Lobotka, Anguissa; Politano, Raspadori, Kvaratskhelia
Union Berlin possible starting lineup:
Ronnow; Bonucci, Leite, Knoche; Juranovic, Khedira, Laidouni, Gosens; Becker, Behrens, Fofana
We say: Napoli 2-0 Union Berlin
To say that Union Berlin are totally devoid of attacking inspiration would be unfair, as the Iron Ones troubled the Napoli backline on several occasions two weeks ago, only to be let down by poor finishing.