Salah was substituted during Egypt's 1-1 draw with Iran in their final group match, casting doubt over his availability for the knockout tie in Dallas.
Photos posted on the Egyptian Football Association's Facebook page showed a smiling Salah back on the training pitch in Spokane, where Egypt have been preparing for the Australia match. The team accompanied the images with the caption: "The King is back".
Salah's return was a timely boost for Egypt, who progressed to the knockout stages for the first time after finishing second in their group with five points, behind leaders Belgium on goal difference.
The 34-year-old has been instrumental in Egypt's campaign, scoring once and providing two assists.