South Africa allrounder Ryan McLaren will miss the second Test due to concussion brought about by a brutal Mitchell Johnson bouncer.

Wayne Parnell is expected to take McLaren's spot in the XI for the clash in Port Elizabeth that starts on Thursday.

Johnson opened up a cut behind McLaren's ear on day four of the first Test when he struck him on the side of the helmet.

Captain Graeme Smith joked after Australia completed a 281-run victory on Saturday that McLaren looked like he'd been scrummaging in a Super Rugby match and was in good spirits.

But the 31-year-old started to experience concussion-related symptoms including worsening headaches and nausea on Sunday night.

He was admitted to a clinic and remains in doubt for the rest of the three-Test series.

"He is doing much better and has been discharged but from a medical protocol point of view, any form of concussion is concerning enough to rule him out of the next Test match," Proteas team manager Mohammed Moosajee said.

"He will be monitored over the next four to five days and will have further assessment done on Monday to decide whether or not he can join up with the squad prior to the third Test in Cape Town."

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