Partenopei have a mountain to climb in next week's second leg after falling to a 3-0 loss in the Czech Republic.
Mazzarri revealed that he will be holding a team meeting tomorrow to discuss the lacklustre performance.
"Some players didn't step onto the field the right way," Football Italia quotes Mazzarri as saying.
"We need to get out there with another approach. You could see we didn't have the right mentality. It seemed almost as if Viktoria were here for a kickabout and wouldn't have bothered us.
"We cannot step on to the pitch like that. Tomorrow I will have to speak to the lads and hear from the horse's mouth what went wrong."
The 51-year-old said that he is hoping his team can do what Chelsea did to them in the Champions League last year by staging a stirring comeback.
"I want to remember what happened with us against Chelsea last season in the Champions League, as they seemed done for too," he added.
The Blues came back from a 3-1 first-leg defeat in Naples to progress 5-4 on aggregate.