Australia U20s centre Campbell Magnay has been suspended for two matches.
Magnay was sent off in Australia's opening World Championship match against Scotland on Wednesday morning, after two yellow cards.
The first came in the sixth minute, for a tip tackle on Scotland's Matt Smith, with the second a 45th-minute neck roll.
Australia appealed the first yellow card in tribunal overnight, but it was upheld in review.
The decision means Magnay will miss Australia's final two pool matches, against Italy and England, which will determine their fate in the competition.
Australia takes on Italy on Saturday night, at 10:30pm AEST, LIVE on FOXSPORTS.