It's a tie that could have far wider reaching consequences for both their coach Andre Villas-Boas and English football as a whole.
Villas-Boas, for many people's money, is living on borrowed time in the Stamford Bridge hot-seat.
Rumours of dressing room dissent and some unsatisfactory results have made his position appear precarious.
Chelsea face a fight to finish in the top four in the Premier League, battling alongside Arsenal and Newcastle for that crucial fourth spot, and hence qualification for next season's premier European club competition.
They came close to bowing out of the FA Cup at home to Championship Birmingham City at the weekend too, before snatching a draw.
Villas-Boas admits he doesn't know if he will still be in a job if they fail to beat the Italians.
"It's not up to me to decide that, you have to ask that question to the right person," he said, referring to owner Roman Abramovich.
But the Portuguese manager says his side is lacking in belief due to their recent poor results.
"The situation is we don't have enough good results for us to feel a bit strong," he said.
"But we are still in these competitions and will continue to push for them. It will be a difficult game against Napoli but we have shown in the group games we can overcome adversity."
Chelsea went into their final group game at home to Bayer Leverkusen knowing that if they didn't win they risked crashing out.
They did win 2-0 and topped the group but now there is the added pressure that they are realistically England's last representatives.
The dominant teams in this season's Premier League, Manchester rivals United and City, both crashed out in the group stages while Arsenal's 4-0 thrashing at AC Milan last week even had their manager Arsene Wenger admitting they had no chance of progressing.
With Chelsea's recent troubles and Napoli's return to form -- they have won their last two games following a sticky period marked by numerous draws -- the Italians' coach Walter Mazzarri is feeling confident.
"Right now maybe Chelsea are worse than us but I don't believe that," he said. "At this level you come up against teams full of great players who are used to certain situations.
"I'm sure they'll regroup for the occasion. But in any case it always depends on the unique moment, you also need the good fortune to be playing them in their worst (moment)."
Napoli have the good fortune of themselves being in the ascendancy.
"Right now all the incidents are going well whereas before everything went badly," he added.
"We've always played well, we've almost always dominated our opponents but we've only had bad luck.
"Sometimes we conceded goals from their first attack but this time it was us who did it both against Fiorentina (3-0) and Chievo (2-0)."
Mazzarri will be forced to watch from the stands having been sent off in their last group game against Villarreal.
He may also be without centre-back Hugo Campagnaro while Chelsea have their own defensive worries with captain John Terry rated as doubtful and left-back Ashley Cole facing a race to be fit.
Source: AFP
Source: AFP