Smith had made 80 on the fourth day when he was struck by a short ball from fast bowler Jofra Archer
Australia’s coach Justin Langer said there may come a time when batsman Steve Smith has to wear a neckguard on his helmet whether he likes it or not after the star batsman was felled by a bouncer in the second Ashes Test against England at Lord's on Saturday.
Smith had made 80 on the fourth day when he was struck by a short ball from fast bowler Jofra Archer, timed at 92.4 mph (148.7 kph), on an unprotected part of his neck.
Smith, who fell to the ground, retired hurt after receiving onfield treatment.
But after just 46 minutes away, he returned at the fall of the next wicket before he was lbw to all-rounder Chris Woakes for 92.
That dismissal denied Smith his third hundred in as many Ashes innings after he marked his comeback Test following a 12-month ball-tampering ban, with scores of 144 and 142 in Australia's 251-run win at Edgbaston.
Significantly, Smith was wearing a helmet without the additional stem guard neck protection introduced following the death of Phillip Hughes after his former Australia team-mate was hit by a bouncer in a 2014 domestic Sheffield Shield match in Sydney.
"He (Smith) just doesn't feel right (wearing a stem guard)," said Langer. "I know they came in after the tragedy of Hughesy. He might rethink it now after seeing what happened today, but you'd have to ask him that. At the moment, the players have a choice and I wouldn't be surprised if they become mandatory in the future."
Former Australia batsman Langer was hit on the head several times during his Test career, including on debut by the West Indies' Ian Bishop at Adelaide in 1993.
But the 48-year-old was confident Saturday's blow would not do lasting damage to Smith's confidence against fast bowling.
"When you get hit, it's always in the back of your mind," said Langer. "Any batsman who tells you it's not is a liar. But he (Smith) is also the sort of person who will do everything from now until the next time he bats — whether it's mentally, visualising or practising — to be right."
This series has seen the introduction of concussion substitutes, who can replace a batsman who has a severe head or neck injury.
But Langer insisted Australia had not taken an undue risk in allowing Smith to resume his innings.
"He passed all the testing and that's why he came back out," he said. "These are like my sons alright, so you're never going to put them in harm's way, even though you're always in harm's way with Test cricket. What else do you do? The medicos cleared him, he wanted to get out there."
Before this match, Langer said Australia would look to test Test debutant Archer's resilience.
The World Cup winner, in for the injured James Anderson, rarely let up, however, during a fine return of 2-59 in 29 overs.
"I've got massive admiration for Jofra," Langer said. "But I did say, like all bowlers, Test cricket is really hard. His endurance was outstanding today, his skill, his pace. To be able to bowl 29 overs today, what a great effort. Time will tell whether that has an impact."
Smith's 92 helped Australia close to within eight runs of England's first-innings 258.
Australia quick Pat Cummins then took two wickets in two balls, including dismissing England captain Joe Root for a golden duck.
At stumps, England were 96-4, a lead of just 104 runs.
Australia could yet now force a win that would put them 2-0 up with three to play even though five sessions in the match have been washed out.
"My thoughts are this is why we love Test cricket so much," said Langer. "We've lost a couple of days — or nearly a couple of days — to rain and it's absolutely game on tomorrow."