Struggling paceman Vernon Philander isn't a green-top bully despite still seeking his first wicket in Australia, South African captain Graeme Smith says.

Smith backed Philander to find form as the Proteas made two changes for the second test against Australia starting on Thursday in Adelaide.

Allrounder Faf du Plessis will make his test debut replacing injured batsman JP Duminy and legspinner Imran Tahir was recalled at the expense of fast bowler Rory Kleinveldt.

Smith defended Philander, who returned unflattering figures of 0-103 in the first test following a wicketless tour game against Australia A.

The Proteas' skipper laughed off a suggestion that Philander, who took 63 wickets in his initial 10 Tests before arriving in Australia, was a green-top bully.

"We didn't have any green tracks in England and he did pretty well," Smith told reporters on Wednesday.

"I have liked the way he has looked this week ... he has had some really good zip in the nets, the ball has been swinging and moving, and I expect good things from him."

Smith said a downturn in Philander's fortunes after a stunning start to his test career was "the nature of the sport we play".

"He has had such an incredible run to his test career, there is bound to be tough games along the way," he said.

"And I think he has certainly got the character to bounce back from that.

"I don't think he bowled really badly in Brisbane. He still created a couple of chances that could have easily gone to hand."

Smith said Pakistan-born spinner Tahir would concern the five left-handed batsmen in Australia's top seven because of his threatening wrong'un.

"Hopefully, there is a lot of rough - not for me - for the Australian left-handers," Smith said.

"He certainly has used rough well in the times that he has played for us and he created a lot of stress for (England batsman Andrew) Strauss and the left-handers in England - the wrong'un turning away is not a bad option."

Du Plessis, a right-handed batsman who also bowls legspin, won a test cap aged 28.

"The fact that he is making his debut is exciting. It's a wonderful opportunity for Faf," Smith said.

"He has played a role in the one-day formats and the Twenty20 formats and I know he's really excited to get the opportunity to play test cricket.

"He has been around this group now solidly since England and he has been a part of some special times, so I think he's looking forward to hopefully making a mark on this team."

- AAP