Australia won't risk vice-captain Shane Watson in the second cricket Test against South Africa starting Thursday, captain Michael Clarke says.

Watson missed the drawn series opener with a calf injury and attempted to prove his fitness at training in Adelaide this week.

But Clarke says lingering doubts about the Watson's injury prompted Australia to name an unchanged team for the second Test.

"He improved a lot over the last few days ... but is probably a few days short of being 100 per cent,'' Clarke told reporters.


Left-arm paceman Mitchell Starc will again be 12th man, Clarke said.

Australian squad:
Michael Clarke (capt), David Warner, Ed Cowan, Rob Quiney, Ricky Ponting, Mike Hussey Matthew Wade, Peter Siddle, James Pattinson, Nathan Lyon, Ben Hilfenhaus, Mitchell Starc (12th man).