Napoli capitalised on Lazio's 2-1 loss at Empoli, moving into third position in Serie A thanks to Gonzalo Higuain's 61st-minute goal at the Stadio Artemio Franchi.
Higuain netted his sixth Serie A goal in four games as Napoli extended their unbeaten run in the league to eight matches.
"I had said Fiorentina were a very strong side and we saw that was true, but even then we had 10 counter-attacks that could've done more damage," the Spaniard said.
"Tonight we saw some important notes and the really positive aspect is that we can still improve.
"Winning here is not easy, but we achieved it and must now focus on preparing for Cagliari."
"Insigne has sprained his right knee with ligament damage. Tomorrow morning he will undergo the necessary tests," Napoli announced in a statement.
