Premier Australia batsman Steve Smith, who was ruled out of the final day proceedings of the second drawn Test at Lord's following a concussion, is hoping to regain full fitness before the third Ashes game beginning Thursday.

A ferocious bouncer from England's Jofra Archer had floored Steve Smith on Day 4 of the rain-affected second Ashes Test at Lord's on Saturday. However, he returned to the field after clearing the concussion Test and  made a fighting 92. Before the fifth day's play, another concussion test was conducted in which Smith reported grogginess and a headache.

"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."

ICC match referee Ranjan Madugalle then approved  Marcus Labuschagne as Smith's replacement with no conditions attached after Australia applied for a concussion substitute following Steve Smith's injury. It was the first time a concussion sub has ever come into a Test match.

"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."

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.