However, he has made a slow start to life at Stadio San Paolo – scoring just once in four Italian top-flight games – which came against Atalanta on October 17.
He made his Europa bow against Dutch side AZ Alkmaar, albeit, the Nigerian could not rescue the Blues from losing 1-0 at home.
With the Italians in dire need of a victory against the Spanish top-flight side at Reale Arena, manager Gattuso has made some changes to his team with 25-year-old forward Andrea Petagna taking the place of Osimhen.
Also missing in the starting XI are Dries Mertens, Hirving Lozano and Fabian Ruiz. Nevertheless, Napoli boss kept faith in Kalidou Koulibaly to anchor his defence line with goalkeeper David Ospina staying in goal.
"It's a really important game. There are another 15 points to play for,” Gattuso said during Wednesday’s pre-match game.
"We'll change a few things around tomorrow but we'll put out a very strong side.”
The 42-year-old also said his team will not worry about Silva, insisting Sociedad have got a depth of quality in their squad.
"David Silva is not the only problem we have to worry about. They have lots of good young players They're a quality side who know how to scrap,” he continued.
"We know how we want to play tomorrow. We need to play well not just from a technical point of view but as a team.
"We have a duty to give our all in every competition. Real Sociedad play good football. It's no coincidence they're top of La Liga."
REAL SOCIEDAD (4-1-4-1): Remiro; Gorosabel, Elustondo, Le Normand, Monreal; Guevara; Portu, David Silva, Merino, Oyarzabal; Willian Jose.
NAPOLI (4-2-3-1): Ospina, Di Lorenzo, Maksimovic, Koulibaly, Mario Rui; Demme, Bakayoko; Politano, Lobotka, Insigne; Petagna.