Victory at the Juventus Stadium against Czech Republic in Turin - which is hosting its first-ever Italy game - would guarantee the four-time world champions a place at next year's finals in Brazil.
The Italians, who remain unbeaten in qualifying, were made to suffer but edged Bulgaria 1-0 on Friday, courtesy of veteran striker Alberto Gilardino's goal, to go seven points clear at the top of Group B with three games remaining.
"We are one step away from the World Cup," Prandelli told reporters. "But right now every game is complicated as we are not at our best from a physical standpoint.
"The game against the Czech Republic is not going to be a walk in the park. We will have to suffer just as we did against Bulgaria.
"We will, however, have an extraordinary motivation to win on Tuesday."
The Azzurri have won five of their seven qualifying games and will be bolstered by the return of AC Milan playmaker Riccardo Montolivo as well as strikers Mario Balotelli and Dani Osvaldo - all returning from suspension.
But Italy, who are without injured defenders Ignazio Abate and Luca Antonelli, can expect a stern test against a wounded Czech Republic side.
The Czechs conceded a stoppage-time goal to lose 2-1 against Armenia in Prague on Friday.
The result marked only their second defeat in qualifying and left the Czechs one point behind second-placed Bulgaria and level on nine points with Armenia and Denmark.
"We are in a complicated situation," Czech coach Michal Bilek said. "Now we have to win all of our games, including the one against Italy."
Bulgaria, meanwhile, will be looking to bounce back from their first defeat in qualifying when they take on bottom-side Malta in Ta' Qali.
Luboslav Penev's side did manage to hold on to second spot nevertheless and he said: "We will try to win our games.
"There are still three matches to go but with this result the Czech Republic certainly have less chance of qualifying, which can be an advantage for us.
"We must continue to believe, as the World Cup target is still within our reach."
Tuesday's opponents Malta have lost six of their seven games in qualifying, with their latest setback arriving in the form of a 2-1 loss to Denmark.
The Danes will be looking to give an improved performance when they travel to Yerevan to face Armenia.
The last time both teams met was in June and the Armenians equalled the biggest win in the country's history with a shock 4-0 triumph over Denmark in Copenhagen.
Armenia go into the reverse encounter on the back of two consecutive away wins that have placed them firmly in contention for a play-off place.
The hosts will be hoping to recover Spartak Moscow midfielder Aras Ozbilis, who is currently doubtful with a knee injury.
"Everything depends on Aras' participation in the game," Armenia coach Vardan Minasyan said.
"He is a very important player for us."
The good news for Minasyan is that Dynamo Moscow goalkeeper Roman Berezovsky has shaken off a muscular injury and is expected to feature.