The 36-year-old's inclusion as the only recognised out-and-out striker in Germany's World Cup squad has been met with criticism from some, but his 2002 World Cup team-mate has backed him.
The Poland-born Lazio man underwhelmed at club level in Serie A this season, scoring seven times in 25 appearances as the Rome side finished ninth.
Nevertheless, a goal in Friday's 6-1 win over Armenia made Klose Germany's all-time leading scorer, taking him one ahead of Gerd Muller's previous record of 68.
Now Klose has his eyes on Ronaldo's record as the leading goalscorer in World Cup history, needing just one to go level with the Brazilian on 15 and Bierhoff is certain the forward can be decisive for Germany.
Bierhoff said: "As far as Miroslav Klose is concerned, I am convinced that he will play an important part at this World Cup.
"Whether or not he will play the full seven matches of 90 minutes, is another matter.
"But he is crucial to our attack and it's also crucial that position of a real number nine to be filled, and he's the ideal player to fill that position.
"But, having said that, it doesn't really matter what kind of number players wear on their shirts, but what running patterns players have and whether they actually get into the rivals' penalty box."
Bierhoff also discussed Germany's target for the tournament and the former Milan man said reaching the final was their aim.
The 46-year-old added: "How long will we stay here? I hope obviously we can stay here until the final.
"In my head, and at home, I used to say 'OK, darling, I'll be gone for the next five to six weeks'.
"We're just not thinking about anything else, but that is our philosophy when it comes to planning ahead."
