The hard-running midfielder sustained the injury in the sixth minute of Australia's 34-31 loss to Argentina in the Rugby Championship on Saturday when Pumas fullback Emiliano Boffelli crashed into him as he scored a try.
Ikitau played on but was forced to leave the pitch 12 minutes later in obvious pain. Scans confirmed a fracture that will make him unavailable for Australia's next two tests against New Zealand and a World Cup warm-up against France.
The Australian, who has played 28 times for the Wallabies, was one of the best Australian players in this year's Super Rugby Pacific competition.