Mazzarri is revelling in Napoli's progress to the knockout rounds after 22 years away but was keen to point out that the Londoners had far more European experience despite their domestic woes.
"Now we are simply happy to be here playing two matches against a Chelsea side that have played more than 100 games in this competition and this says a lot," Mazzarri, banned from the dugout for pushing an opponent in the group stage, told a news conference on Monday.
"It seems strange to me that people are saying we are favourites.
"I hope they are not at their best because they have lots of decisive players."
Napoli have also not been in great form in Italy's Serie A, having been outside bets for the title at the start of the season. They lie sixth but shone in Friday's 3-0 win at Fiorentina where strikers Edinson Cavani and Ezequiel Lavezzi both scored.
"We prepare for the game beforehand. I'm sorry I can't be on the bench but (assistant Nicolo) Frustalupi is perhaps better than me as a tactician," he said.
