Australia have called up Jake Gordon as a replacement for fellow scrum-half Will Genia, who will be out of action for six weeks with a broken arm.
Genia underwent surgery on Sunday after suffering the injury during the second Test against Ireland in Melbourne on Saturday, a match the tourists won 26-21 to level the three-match series.
His absence is not only a blow for the Wallabies ahead of a decider in Sydney but also the Melbourne Rebels, with the 30-year-old now likely to sit out the remainder of the Super Rugby season.
Gordon has flown back from Japan - where he had played in an exhibition match for the Waratahs - to join up with the squad.
However, head coach Michael Cheika is expected to promote Nick Phipps to the number nine shirt in Genia's absence.