Australia meets South Africa in the first of a three-Test series starting at the WACA Ground on Wednesday.
Clark said the injury, caused by throwing, could end his summer and may require surgery.
The bowler was visibly distressed at the WACA today.
He said he would fly home to Sydney later today and make an appointment with orthopaedic surgeon Greg Hoy.
Hoy successfully operated on skipper Ricky Ponting (wrist) and all-rounder Andrew Symonds (shoulder).
India toppled Australia to achieve their highest-ever ranking of second in the ICC ODI Championship table courtesy the series victory in New Zealand and the world champions' recent dip in form.
