Smith did not come on to field on day four in Durban, after being on the side of the helmet by a short ball from South African speedster Anrich Nortje while batting in the morning session.
The 37-year-old was assessed on the field and passed a test, appearing unfazed as he reached 27 in Australia's pursuit of quick runs.
However Australia opted to keep him off the field in case there had been a concussion, and conduct further tests. As of stumps, Smith had not failed any.
The world's No.2-ranked batter is expected to be tested again on Tuesday morning in Durban, and will continue to be assessed for as long as Australia see fit.
Smith has previously battled concussions, most famously when he was struck in the head by Jofra Archer during the 2019 Ashes.
While the early signs are good, any concussion would leave Smith in serious doubt for Sunday's second Test in Gqeberha given the tiered-return protocols.Â
It would also add to the quandary around the make up of Australia's side for that match.
Josh Inglis is back in South Africa after his fractured finger, batting in the nets wearing a splint on Monday and offering every sign he will be available for Sunday.
Cameron Green is also recovering from an abdominal strain, and not yet ruled out of the second Test.
Either of the pair would likely have batted at No.5 in this Test if fit, but Matt Renshaw's scores of 190 and 82 have made the case for him to stay there.
That would likely require Nic Maddinson to remain as opener, with his hard-swinging 48 on Monday at least help making the case for that.
The other option would be for one of the pair to come in for Beau Webster, who had his most substantial innings of the past three Tests with an unbeaten 39 on Monday.
It followed scores of 12, 5 and 0 against Bangladesh in August, before being caught behind for four off his second ball in the first innings in Durban.
The Tasmanian allrounder remains batting at No.7, with his value with the ball potentially increased by the fact Green is unlikely to bowl in this series.
"There is obviously going to be some conjecture going into every Test with what the line up is," Webster said.
"I got a start in this Test and am looking to contribute wherever I can, with bat, ball or in the field.
"When picked I will be doing the best to do the best I can to win games for Australia."
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