'Steve has been closely monitored by medical staff overnight and this morning reported that after sleeping well, he woke with ´a bit of a headache and a feeling of grogginess´,' said an Australia team spokesman.
Smith was felled when a Jofra Archer bouncer struck his neck on Saturday.
"Steve has been closely monitored by medical staff overnight and this morning reported that after sleeping well, he woke with ´a bit of a headache and a feeling of grogginess´," said an Australia team spokesman.
The series is the first being played under the International Cricket Council´s new concussion substitute regulations, part of the inaugural World Test Championship, which allow players who have suffered head or neck injuries to be replaced fully by a substitute, who was previously restricted to fielding alone.
Marnus Labuschagne, on the field as 12th man when play resumed Sunday, became the first concussion substitute in Test history after Australia´s request was approved by match referee Ranjan Madugalle.
Labuschagne can now bat or bowl in Smith´s place if required.
There are doubts whether star batsman Smith will feature in the third Test at Headingley starting on Thursday, with the spokesman saying "the short turnaround is not in his favour".
Smith was hit by an Archer bouncer when on 80 on Saturday and retired hurt.
He resumed his innings at the fall of the next wicket after 46 minutes off the field, and was eventually out for 92 -- the first time this series he had been dismissed for fewer than 100 runs.
The spokesman added: "Steve reported that his left arm which was also struck (by Archer) during his innings yesterday was ´much better´" and that as part of further testing on Sunday, Smith "demonstrated some deterioration".
"On that basis Steve has been withdrawn from the match by team doctor Richard Saw," the spokesman said.
Explaining how Smith had been allowed to resume his innings, he said: "It is not uncommon for players to pass their tests and feel well on the day of an injury and then display symptoms 24-48 hours later.
"Steve´s fitness will be assessed on an ongoing basis.
"Steve will undergo a precautionary scan on his neck on Sunday."