The Wallabies will enter their final World Cup pool match against Portugal without a back-up playmaker after Carter Gordon was a late withdrawal with a knee injury.
Gordon, who was set to start on the bench as cover for five-eighth Ben Donaldson, has been replaced by Samu Kerevi.
Without another No.10 in the line-up or Wallabies squad, they will likely have to rely on shifting Andrew Kellaway from fullback should Donaldson be forced off.
The injury to Gordon isn't believed to be serious, with the 22-year-old at the Wallabies' final training run where he didn't appear in any discomfort before the session was closed to the media.
The Australians need to win the Saint-Etienne match on Sunday (Monday AEDT) with a bonus point to remain alive in the tournament.
Fiji have the chance to eliminate the Wallabies next round and move through to the quarter-finals, as long as they secure a single bonus point against Portugal, win or lose.