The fast-bowling attack that has been unchanged in Australia's past seven Tests will be hard-pressed to make it eight in a row in the third Test in Cape Town.

The absence of a reserve seamer for the second Test meant that across the first three days Mitchell Johnson, Ryan Harris and Peter Siddle collectively bowled a whopping 121 overs, with their team in the field for almost 200 overs.

In the past three years Australia has only fielded more than 200 overs in a match on three occasions. In each, one of its bowlers succumbed to injury.

When South Africa kept Australia in the field for almost 273 overs in Adelaide in November, 2012, paceman James Pattinson sustained a rib injury that sidelined him for almost two months. When Sri Lanka survived until the 229th over in Hobart in the following month swing bowler Ben Hilfenhaus was sidelined during the match with a side strain. Australia's next-longest stint over that period, just over 214 overs at Lord's in the winter Ashes series, was followed by the diagnosis that Pattinson has stress-fractures in his back after bowling 40 overs.

As South Africa coasted beyond 300 runs and 100 overs in its first innings, Australian captain Michael Clarke began preserving his strike-bowlers Johnson and Harris, using them for a total of three overs in the last 40 of the innings. In the second innings the captain kept them to short spells, with Siddle and off-spinner Nathan Lyon doing most of the bowling.

With the series-ending Test in Cape Town beginning on Saturday, the Australian hierarchy's focus will be whether it will have to call on its reserve pacemen, Pattinson and Jackson Bird, because of the quick turnaround, and on whether Shane Watson has done enough bowling in training to be ready to return.

Clarke said after day three that he was unsure about Watson's availability.

''I spoke to Watto today. I did some work [in the nets] during the lunch break and he was out there bowling then,'' Clarke said. ''He's certainly improving.''

Clarke said his incumbent pacemen had been made to work ''extremely hard'' in Port Elizabeth and reiterated his preference for Australia to boast a seam-bowling all-rounder in its team.

''Ideally, 'Boof' [coach Darren Lehmann] and I have said for a while, in a perfect world you'd like everyone in your team to be able to bowl, especially when you get slow wickets,'' he said.