The Scottish giant sits second in Group G behind Barcelona after garnering seven points from four outings and will qualify for the knockout stages with a win over the Portuguese side.
A score draw will also be enough to seal a round-of-16 place for Celtic if Spartak Moscow fails to beat Barcelona in the other group game.
"I believe this game [against Benfica] is crucial for both teams. Qualification [to the knockout phase] is within our sights and realistic," Wanyama told Goal.com.
"But we are motivated and confident, nobody gave us a chance in this group and [also] against Barcelona. So we need to continue with what we have been doing."
Wanyama, who was voted man of the match during last weekend's league match against Aberdeen, has been in exceptional form this season and earned rave reviews for his goal that set his team up for a historic victory against Barcelona in their last European tie.
Barcelona has nine points, while third-placed Benfica is three points behind Celtic, with the Russian side sitting fourth in the group a point behind Benfica.