Walter Mazzarri's men made a solid start to the 2014-15 campaign, winning two and drawing two of their opening four league fixtures - including a 7-0 hammering of Sassuolo.
However, they were brought back down to earth in the two games before the international break, receiving 4-1 and 3-0 beatings from Cagliari and Fiorentina respectively.
Former Napoli boss Mazzarri was subjected to the ire of the crowd following the loss to Cagliari at San Siro but Icardi - who has seven goals to his name in all competitions this season - believes the backing of the home fans can spur them to victory this weekend.
"We need the help of the San Siro crowd," Icardi told Gazzetta dello Sport.
"Don't whistle - instead cheer for the team and for the coach. Against Napoli I'm convinced we'll have support for 90 minutes."
Inter owner Erick Thohir has echoed the sentiments of the Argentine striker as he looks to alleviate the pressure on Mazzarri.
"We must be the 12th man on the field, that will make a difference," he said. "San Siro stadium is unique in the world. The coach and the team are waiting for you all Sunday at the stage to collect the embrace of the Inter fans. Forza Inter."
By contrast, Napoli - coached by ex-Inter boss Rafael Benitez - had started to find form before the international games, claiming back-to-back victories over Sassuolo and Torino following a three-match winless streak.
Lorenzo Insigne found the net in the 2-1 success over Torino last time out, and the diminutive forward is dismissive of any talk of problems at Inter.
"I do not think Inter are in crisis," he told Radio Kiss Kiss. "They have great players and a very good coach that we know well.
"At San Siro we have to play a great game because we will have to face a strong team. We want to continue on the positive path and extend the streak of success."
Napoli wll be without midfielder Walter Gargano, who is set to have surgery on a fractured cheekbone picked up in training, while Inter have doubts of Mateo Kovacic, who limped out of Croatia's 6-0 win over Azerbaijan on Monday with a groin injury.
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