Australia’s growing casualty count is boosting South African confidence, despite the home side holding the whip hand in the Boxing Day Test.

But on a day two with injuries aplenty, the most surprising one had nothing to do with the play, as Proteas paceman Anrich Nortje was knocked over by Spidercam.

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The wire-guided Spidercam, which hovers above the players, went too low and collected the paceman from behind as he was fielding.

Nortje was able to bowl at the start of day three, but he was monitored for soreness in his left shoulder and elbow, which took the impact as Nortje was knocked to the ground on day two of the Test.

The camera hit Nortje at some pace, but he was on his feet immediately and was able to keep bowling.

While Nortje had to leave the field later, it was because of cramp as the players roasted in the mid-30s conditions.

Spidercam was not used for the rest of the day and its operators spoke to the South Africans, with the incident blamed on human error.

“I didn’t know what hit me. The one thing we’ve spoken about earlier is how low it is,” Nortje said.

“I don’t think it should be travelling head-height.”

The tourists trailed by 197 runs after day two at the MCG, and their last seven Test innings have all finished below 200.

But the in-form Australian bowling attack could be down one or two key members for South Africa’s second visit to the crease.

Australian coach Andrew McDonald spoke to ABC Radio ahead of day three. 

He confirmed Cam Green will not bowl, but Mitchell Starc will take full part in the rest of the match, both batting and bowling, despite injuring his left middle finger while fielding on day one.

However, it is not clear how much bowling he will be able to get through, given his injury.

A close-up shot of a cricketer's hand, with the middle finger heavily bandaged, as a coach examines it with his finger.
Mitchell Starc is managing a finger injury, and it’s unclear how much he will be able to bowl in South Africa’s second innings.(Getty Images: Darrian Traynor)

“We’re just working with medical staff with him for this Test, but it’s likely [Starc will] miss [the Sydney Test],” McDonald said.

“We had planned to discuss the squad for Sydney last night but a few things came up.

“It’s likely a spinner will be added.”

The index finger on Green’s right bowling hand was bloody and swollen on Tuesday after a delivery from paceman Anrich Nortje jammed it against the bat handle.

An Australian cricketer leaves the field with his head down, flanked by two medical officials during a Test match.
Cameron Green became the second Australian bowler sent for scans during the Boxing Day Test after he retired hurt on day two.(Getty Images: CA/Daniel Pockett)

Green was forced to retire hurt and went to hospital for scans.

“That’s going to be a big factor,” Nortje said of the Australian injuries.

“It’s going to be crucial to bat for as long as we can.

“The more overs the bowlers are to bowl, the more maybe a backup bowler … would have to apply themselves.

“That’s going to be a crucial stage for us … work through the difficult stages with our top order and then try and cash in a little bit later.”

Nevertheless, Australia will resume on Wednesday full of confidence at 3-386 as they close in on their first home Test series win over South Africa in 17 years.

Rain is forecast for Wednesday after Tuesday’s oven-like temperatures, when several players, including Nortje, suffered with cramp.

After starring with 200 in his 100th Test, Australia opener David Warner had to retire because he was so affected by the conditions.

He returned to bat on day three after the fall of the fifth wicket, but was immediately bowled by Nortje. 

On Tuesday the misfiring South African top order baked in the field ahead of an attempt to rally in their second innings.

A year ago, Victorian fast bowler Scott Boland exploited home-ground conditions brilliantly on his Test debut to rout England in the second innings of the MCG Ashes meeting, taking six wickets.

If Starc and Green are out of action, Boland and captain Pat Cummins will shoulder the bowling burden along with off-spinner Nathan Lyon.