"Were it not for our intervention, the game against Real Madrid probably wouldn't be played because the San Paolo wouldn't meet criteria," city mayor Luigi De Magistris told Radio Crc on Thursday.
The San Paolo, where Diego Maradona helped the southerners to their sole league titles in 1987 and 1990, is one of the most emblematic football venues in Italy.
With a total capacity of just over 60,000, it is also the third largest after the San Siro (81,277) in Milan and the Stadio Olimpico (72,698) in Rome.
But the venue, built in 1959 and still owned by the city council, is in dire need of refurbishment.
Club president Aurelio De Laurentiis is backing plans for a new, 20,000-seater stadium to host the Serie A side, who sit third in Serie A nine points behind leaders Juventus.
But De Magistris fully intends to refurbish the existing structure, even if it means necessary repair works are carried out piecemeal fashion and exclusively at the expense of city coffers over a four-year period.
Last week, Napoli lost their last 16 first leg 3-1 at the Santiago Bernabeu stadium in Madrid and host the Spanish giants for the return leg on March 7th.
"We won't build a new stadium, but we'll do a great job renovating the existing stadium," De Magistris added.
"Our next objective is to finish the dressing rooms, the corridors and the media tribune for the Real Madrid game.
"We'll respect that commitment, even without the support of the club."
Although the majority of stadiums across Europe are owned by clubs, most in Italy belong to the local authorities. In Serie A, only the stadiums used by Juventus, Sassuolo and Udinese are owned by the clubs.
Amid a wave of new stadium developments in the 1990s and 2000s, Italy was largely left behind. The San Paolo, which had an initial capacity of nearly 110,000 when it was built over a 11-year period from 1948-1959, is one example.
De Magistris said the city was committed to completing its full refurbishment, whether De Laurentiis wants to contribute or not.
"The city is committed to sport and, with a great deal of sacrifice, we'll complete this. In other cities, this is usually done by the club," he said.
After knocking the corridors, media tribune and dressing rooms into shape for the arrival of Zinedine Zidane's 'Galacticos', De Magistris said more work will be carried out.
"In the summer we'll focus on other repairs, the toilets, the seats and a few other things."
He added: "Between now and 2021, whether the club (Napoli) invests in the stadium or not, we will put aside the necessary funds to completely restructure the stadium.
"A 20,000-seater San Paolo would not be practical. The stadium is for the people, and I'm firmly opposed to those who want to put up economic barriers to stop people from accessing it."
By Justin Davis