Slovakia are bottom of the group with one point but could still qualify for the second round if they beat the Azzurri and New Zealand take no more than a point against Paraguay.
"We will do everything to get through. We want to be bold but we have to be rational because our opponents are the world champions," Weiss told a news conference on Wednesday.
"All the players are fit and in good physical condition but there will be some changes in tomorrow's lineup."
Slovakia only had one shot on target in Sunday's 2-0 loss to Paraguay so the nippy Miroslav Stoch, back after injury, could come in against faltering Italy at Johannesburg's Ellis Park.
Italian observers know all about Slovakia and Napoli playmaker Marek Hamsik and Weiss is sure he will find form.
"In his first two matches he did not reach his and my expectations. Tomorrow he can shine just like he does in the Italian league," Weiss said.
"We want to surprise them with our boldness."
CUT SHORT
The Slovakia coach acknowledged he had gone too far when he stomped out of a news conference on Monday after spending less than a minute answering questions, the second time in three days he had cut things short after being upset by criticism.
Slovak media also reported he had insulted them as he left.
"I'm sorry for what happened, sorry for our relationship at the moment," he said.
He added that he worked in football to make people happy while some in the media work to make people sad.
Weiss had earlier been in a much friendlier mood than in previous days at Slovakia's final training session in Pretoria.
The coach urged media not to go overboard if they fail to progress in their first World Cup.
"(Don't write about it being) a catastrophe or a shame. Maybe acknowledge that there are some big teams like France who are already at home," he said.
