The Algerian striker joined the club in January on loan from Leicester but arrived with a thigh problem and is yet to make his debut.
The 29-year-old suffered a setback in his recovery in training last week and could now be absent until the end of next month, but boss Benitez believes the forward can still make an impact at St James' Park.
When asked what kind of difference the forward could make to his side, Benitez told the Shields Gazette: "We have to see if he's fit, first.
"If he's fit, we will see. But Dwight [Gayle], Ayoze [Perez] and Joselu, if they continue working like they worked in the week, and then afterwards they score goals, that will be very good.
"He [Slimani] will have to compete for his position. Hopefully, he will be another body and before the end of the season, he will be another one who can help."