Udinese without Di Natale, Sanchez
Di Natale is the league's top scorer with 26 goals so far, but he will be sidelined after an injury suffered during training last week flared up again.
His absence adds to that of Chilean forward Alexis Sanchez, who is still recovering from injury.
Udinese sit fifth in Serie A, having dropped out of the top four - which offers a place in next season's UEFA Champions League - last week.
Napoli are three points behind league leaders AC Milan with six matches remaining. Milan host relegation-threatened Sampdoria.