On Saturday, Smith was hit by a ferocious bouncer on the neck by debutant Jofra Archer and had to retire hurt at 80. However, he came back after passing concussion tests and returned to make 92.
Another concussion test was conducted before the fifth day's play as per Cricket Australia protocol, which "demonstrated some deterioration from his testing which is consistent with the emergence of the symptoms he was reporting."
"It's certainly an area of concern concussion, and I want to be 100 per cent fit," Smith was quoted as saying by BBC Sport
"(It is) certainly up to the medical staff and we'll have conversations."
On Sunday morning, however, the 30-year-old was diagnosed with late concussion and was ruled out of the game and was replaced by Marcus Labuschagne who played a gritty 59-run knock and helped Australia draw the Test and maintain their 1-0 lead in the ongoing Ashes series.
On Sunday evening, CA said a "precautionary scan" of Smith's neck "cleared him of any structural damage" and that he would be "reviewed on an ongoing basis" before the Headingley Test. He also had a scan on his neck on Sunday.
"With the tests that I've done and how I've woken up today, I think it's the right decision," Smith said.
"I'd obviously love to be out there trying to keep performing and try and help Australia win another Test match, but I think the right decision has been made.
"I'll obviously be monitored very closely over the next few days with a pretty quick turnaround in between Test matches and I'm hopeful that I can make a recovery and be ok for that," he added.
Australia won the first Test by 251 runs in Birmingham in which Smith scored twin centuries and proved to be a difference between the arch-rivals.
( With inputs from IANS )
