Napoli missed the chance to cut the gap to Serie A leader Juventus to six points as it was held at Fiorentina to 0-0 on Saturday.
Juventus, which is on a seemingly unstoppable march to a record-extending eighth successive league title, can stretch its lead to 11 points with a win at Sassuolo on Sunday.
Napoli was hit by an early blow in Florence as defender Mario Rui went off with a thigh strain five minutes in and had to be replaced by Faouzi Ghoulam.
Fiorentina goalkeeper Alban Lafont and his Napoli counterpart Alex Meret pulled off a number of fine saves to keep the match goalless.
Napoli seemed certain to score early in the second half but Lafont did brilliantly to parry Piotr Zielinski’s close-range effort.
The visitors were also let down by some poor finishing from Arkadiusz Milik and Dries Mertens.
Fiorentina inched to within four points of a Europa League berth ahead of the rest of the weekend’s fixtures.
Third-placed Inter Milan was playing later and hoping to end its four-match winless streak at Parma.