Hardie, who himself was a replacement for pacer Jason Ralston, suffered a groin injury.
"The ICC has confirmed that the Event Technical Committee of the ICC U19 Cricket World Cup 2018 has approved right- handed batsman and wicket-keeper Patrick Rowe as a replacement player for Hardie," an ICC media release said.
"The replacement of a player requires the approval of the Event Technical Committee before the replacement player can be officially added to the squad," it added.
Three-time champions Australia had halted Afghanistan's dream run with a six-wicket victory in the semi-finals to set up a summit clash with India.
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