Smith retired hurt on 80 after a titanic tussle with Jofra Archer ended with the batsman floored by a 92.4mph bouncer.
There was plenty of deliberation in the middle before the decision was taken to withdraw Smith to undergo further tests, with the batsman apparently keen to continue.
Peter Siddle took Smith's spot at the crease but within 45 minutes the injured batsman was back out in the middle after Siddle had been removed by Chris Woakes.
Smith then added 12 but looked out of sorts and uncharacteristically left a straight Woakes delivery to end his innings on 92.
The batsman then reviewed the decision but didn't wait out in the middle for the final decision, prompting further questions about his state.
But Cricket Australia confirmed he had past assessments before returning.
"Steve was hit on the neck below the left ear. He was assessed lying on the pitch at the instructions of team doctor Richard Saw," read a Cricket Australia statement.
"Dr Saw made the precautionary decision to remove Steve from the field of play to have him further assessed under Cricket Australia's head impact protocol.
"Steve then passed his assessments and will now be monitored on an ongoing basis, as is routine."