Despite Stadio San Paolo being basically a cavernous concrete bowl, the atmosphere at Napoli games is ferocious. The ground will be full by mid-afternoon today, as the fans flood into Curva A and Curva B. Even given the presence of both a running track and, bizarrely, a moat between the pitch and the stands, the roar of the fans should Napoli score will be unlike anything the Chelsea players have heard before.
Even more intimidating, though, will be the whistling if Chelsea have the ball towards the end of the game. The intensity of the noise in the final stage of Manchester City's 2-1 defeat last November was remarkable, seeming almost to repel City's late attacks by its sheer hostility.
The defensive wall
That protection from the crowd is almost unnecessary now, though, because of the quality of Napoli's defence. Unlike most teams that Chelsea face, Napoli play with three centre-backs: usually Hugo Campagnaro, Salvatore Aronica and captain Paolo Cannavaro. If Campagnaro does not recover from a calf injury then Gianluca Grava will play instead. Any combination of three would be exceptionally well organised and disciplined, as well as being comfortable in possession.
It means that when wing-backs Christian Maggio and Juan Zuniga drop back to help, Napoli have a deep line of five defenders which is nearly impenetrable. Twice they frustrated City with it, and Chelsea will sweat to break through it tonight.
The transition to attack
Napoli are probably Europe's fastest counter-attacking side since Cristiano Ronaldo's Manchester United. When they win the ball back, wing-backs Maggio and Zuniga step up, turning their watertight 5-3-2 into a relentless 3-4-3. Like all good sides, they defend as a team and attack as a team. And once their famous front three, the il Tridente of Marek Hamsik, Ezequiel Lavezzi and Edinson Cavani have the ball, they can tear through teams. It is not just that the three are all fast, incisive, imaginative footballers, but that they know each other's game so well that one meets the runs and passes of the others as if by telepathy. Chelsea's defenders can expect a difficult evening.
The Uruguayan spearhead of Napoli's attack is a remarkable mixture of physical and technical gifts. Cavani even gives the impression of a thoroughbred racehorse, with his galloping legs and long mane of dark hair, and would certainly beat every Chelsea defender in a foot race. But he also has teasing movement, ruthless finishing and a perfect first touch to call upon. He scored all three of Napoli's goals against Manchester City in the group stage and has 55 in 77 for Napoli since he joined from Palermo in the summer of 2010.
Marek Hamsik and Ezequiel Lavezzi
Cavani would not be the same without the support of the Slovakian Hamsik and the Argentine Lavezzi, though. Hamsik is a bright runner, who acts as a link between the midfield and the two South American forwards, and chooses his moments perfectly when breaking into the box.
Lavezzi is arguably the finest player of the three. He is a scampering tattooed trickster, combining the waspish energy of his compatriot Carlos Tevez with the imaginative and delightful skill of Juan Roman Riquelme.
He is quicker than he looks, able to burst past defenders from a standing start, and has very well-tuned antennae for seeking out space and danger. He plays just off Cavani, knowing that defenders will soon worry about him and leave his team-mates unguarded.