Nicknamed the Tongan Thor, tighthead Tupou has been one of Australia's best performers this season and had a major impact on the 35-15 Pool C win over Georgia last weekend.
Zane Nonggorr replaced Tupou for the last 10 minutes of the Georgia match in his fourth test and the other tighthead in the squad, Pone Faamausili, has also been struggling with a calf problem.
Australian media reports said coach Eddie Jones was considering switching the experienced and versatile loosehead prop James Slipper to the other side of the front row for the Fiji match.
The Wallabies, who snapped a five-match losing streak against the Georgians, could all but secure a spot in the quarter-finals with a win on Sunday.
Reporting by Nick Mulvenney, editing by Ken FerrisOur Standards: The Thomson Reuters Trust Principles.
Persons:
Denis, Taniela Tupou, Stephanie Lecocq, Tongan Thor, tighthead Tupou, Zane Nonggorr, Tupou, Pone Faamausili, Eddie Jones, James Slipper, Jason Ryles, Nick Mulvenney, Ken Ferris
Organizations:
Rugby Union, Rugby, Georgia, Stade de France, Saint, Fiji, Sunday, Wallabies, Georgians, Thomson
Locations:
Australia, France, ETIENNE, Saint Etienne, Tongan, Georgia