Mazzarri has urged caution from his players, highlighting that Plzen have already pipped Atletico Madrid to top Group B, and admitted that he would play his strongest possible team.
"We are very keen to pass this first knockout round," ANSA quotes Mazzarri as saying.
"Edinson Cavani plays, whether he wants to or not. I need to play the players who make the difference.
"We cannot go all out attack but will have to play carefully. Viktoria is a tough team they won the group by beating Atletico Madrid."
Napoli are currently battling Juventus for top spot in Serie A and are five points behind.