If cricket was a more knee-jerk sport, members of South Africa's Test team may have reason to worry. The cracks are starting to show and some of them could be at risk of falling through.

One Test defeat should not be enough to merit wholesale changes and South Africa are unlikely make them. But it is sufficient for those with alarm bells ringing to stop hitting the snooze button, get up and start performing to allow South Africa to better see how they can move into the post-Jacques Kallis era.

Without him - and it may be enhanced by the Mitchell Johnson effect - the South Africa batting line-up is missing a certain distinction. While Graeme Smith and Hashim Amla's statures are known and celebrated, the top four seems to have shrunk almost overnight in Kallis' absence.

Just consider how Alviro Petersen looked in this last Test. The shot he played to engineer his own demise in the first innings was so unconvincing it prompted a tweet from his namesake Kevin Pietersen about how raw pace can cause a batsmen to do something he otherwise would not. Petersen swished at a ball he should have left, with leaden feet and an unsure mind, to end a nervy 24-minute stint at the crease in which he only managed to score 2.

He lasted even less time in the second dig, nine minutes, and his feet were nothing more than painted on, though it was a better delivery from Johnson. In barely more than half an hour, Johnson had turned Petersen from someone who is usually very sure of himself into someone who is not.

This is not the first time Petersen has seen or faced Johnson. He was up against him in the tour match in 2011, when he had just been dropped from the Test team, on a pitch with more life in it than the rowdy student town that is Potchesfstroom. Despite the variable bounce and Johnson's five-for, Petersen scored a hundred to let the selectors know they had made a mistake by discarding him and when he was recalled, almost a year later, he responded with a century on comeback.

Petersen is mentally tough but his recent run does not show that. He last scored a century 15 innings ago, in January 2013, and since then has an average of 23.92, including a stretch of 10 innings, eight of which were against Pakistan, in which he did not pas 30.

Someone suffering a similar syndrome, although it affects the middle order, is JP Duminy. He has not scored a half-century in seven innings and has not crossed the 30 mark in that time. With increased responsibility on his bowling, in which he takes on the role of a second spinner and sometimes out-bowls the specialist, the focus seems to have fallen off his batting and his talent, as witnessed in the Melbourne Test six years ago, seems to be getting wasted.

There is an option if South Africa want to replace either Petersen or Duminy. Dean Elgar is the extra batsman in the squad and could bat either at the top - where he is comfortable - or the middle, where he has played the majority of his seven Tests. Elgar has the numbers to justify a chance, with a first-class average of 44.14 and 19 hundreds to his name, but it will depend on whether team management think he has the ability to deal with the pressure. Judging by the dropped catch in Centurion, when he was on as a substitute fielder, maybe not.

The same factor will probably continue to leave Quinton de Kock, who despite his first-class average of 48.87 has only played two matches this summer and scored 11 runs, and Stiaan van Zyl, who led the first-class competition run charts until this weekend, out of contention. As Russell Domingo, South Africa's coach, has made clear, a series against Australia, particularly an Australia on the up, is not the time to blood a youngster.

That reason will also mean Simon Harmer, the spinner considered next in line for the role, will have to wait his turn. Robin Peterson is South Africa's third major worry as he continues to struggle to hold up his end but the only other place they can go is Imran Tahir. The legspinner took seven wickets for the Lions in the weekend's domestic match but whether he has gotten over 0 for 260 and whether South Africa want an attacking tweaker are matters that will need to be considered.

Because South Africa picked a squad of 15 at the beginning of this series, they are unlikely to look for answers outside it. If any changes happen, they will probably come from within the group and in the allrounder department. Although Ryan McLaren did what was expected of him, he did not do anything special and South Africa have seen that it will take something extraordinary to beat Australia.

That could open the door for Wayne Parnell, who has been reaching speeds of 150kph this summer and could be their x-factor. His inconsistency has led to him being expensive, though, which will have to be weighed up against the pace he has. Rory Kleinveldt is the other alternative. Although he is not as quick as Parnell, he gets good bounce and he is capable with the bat. It still leaves them with the problem of too many No.8s but Vernon Philander looks ready to move up a spot.

South Africa's knees do not need jerking just yet. They have all the tools they need to come up with an XI that can seal the cracks and continue building their side. But they need to use them cleverly to ensure their Polyfilla is foolproof.