The Bayern Munich striker was absent from the Vatreni's opening-game loss against Brazil last week due to suspension, but he is expected to start in Manaus tomorrow night.
"Mandzukic definitely makes us stronger and you can't replace him like-for-like," Pranjic told FIFA.com. "He's prepared to go out and die for the cause.
"Nikica Jelavic did really well against Brazil but Mario is Mario. We need him. We're a totally different team without him."
Mandukic scored 21 goals for Bayern last season in all competitions.