Italy have not triumphed in any of their last seven matches, a winless run that stretches back nine months, and Prandelli could not hide his disappointment at the final whistle.
Claudio Marchisio gave the hosts an early lead but they wasted chance after chance in trying to double their advantage, and that came back to haunt them as Maxime Chanot earned Luxembourg a draw with a late header.
Prandelli admitted his side had not been good enough, particularly in wide areas, but remained positive about their chances in Brazil.
"We have tried a few things," he told Rai Sport. "But there are a few things we need to improve on.
"At times we were quite crowded in the middle, and had spaces out wide.
"Mario (Balotelli) had two good opportunities in the first half, and had another chance when (Antonio) Cassano came on.
"We've missed a few chances, and then conceded a goal from a corner.
"But we'll keep working. We know we can have a great World Cup."
Italy's opening game of the World Cup sees them face England, who drew 2-2 with Ecuador on Wednesday, before matches with Costa Rica and Uruguay.
