Cricket Australia statement in full: Steve Smith has been closely monitored by medical staff overnight. He slept well but woke up with a bit of a headache and feeling of grogginess. He reported his left arm is much better.
As part of the Cricket Australia concussion protocol, repeat testing was performed this morning and demonstrated some deterioration, which is consistent with the emergence of the symptoms he was reporting.
On that basis, he has been withdrawn from the match. The Australian team will lodge an application for the concussion substitute with the match referee.
In terms of his availability for the next Test, it will be considered over the coming days but the short turnaround is not in his favour. He will be assessed on an ongoing basis and will have a precautionary scan on his neck on Sunday.
Cricket Australia statistics show that 30 per cent of concussions in Australian cricket are delayed. 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.