Australia batter Steven Smith was being assessed for concussion on the fourth day of the first Test against South Africa in Durban after a blow to the helmet from Anrich Nortje.

Smith was pinned on the fourth delivery of his innings on Monday, when a bouncer from Nortje took him on the helmet on the fifth ball of the 13th over of Australia's second innings. The ball ended up flying around to fine leg. As is mandatory, Smith was assessed on the field by the physio and the doctor, while his helmet was changed before he continued his innings. He made 27 off 41 balls before picking out long-on against Simon Harmer.

Smith did not take the field at the start of South Africa's second innings, with substitute fielder Michael Neser fielding in the cordon. Smith had caught brilliantly on the third day, especially with his two takes at slip from reverse sweeps against Nathan Lyon.

A further update is expected on Tuesday. As of Monday afternoon, Smith had not been diagnosed with concussion, but if he was following further assessments, he would need to be symptom-free for a period of time before being available for selection again.

"I've not seen him since I've been off the pitch so I'm hoping he's okay," Beau Webster. "He obviously copped a nasty knock in the head there but wishing him all the best. And hopefully he's back out with us either tomorrow or in the next Test."

There is no real need for Australia to utilise a concussion substitute for the remainder of the first Test, given Smith has finished his batting role and he rarely bowls these days.

Smith has previously suffered multiple concussions in his career, most significantly the fearsome blow he took from Jofra Archer at Lord's in 2019.

Australia have had a number of injuries to contend with on the ongoing South Africa tour. Cameron Green (abdominal strain) and Josh Inglis (fractured finger) were ruled out of the opening Test, resulting in call-ups for Nic Maddinson and Sam Harper. Maddinson was then picked to open in Durban, making his first Test appearance for nearly ten years.

Inglis, who suffered his injury during the first ODI against South Africa last month, rejoined the squad in Durban, and had a bat on Monday. He previously stood-in for Smith last year when he missed the first Test against West Indies in Barbados with a broken finger sustained in the World Test Championship final against South Africa. Cooper Connolly is the other spare batter in the squad.

The second Test against South Africa begins in Gqeberha on October 18.