Smith was forced to retire hurt on 80* after the heavy blow, but bravely returned to bat after passing the concussion tests that immediately followed.
Archer's Test debut could not have been better, but missed out on perfection as Australia stuck on to draw the match, thanks to some defiant batting by Labuschagne and Travis Head.
The immediate assessment can take place on the field, but a full test must take place in a quiet environment such as the dressing room. The unorthodox right-handed batsman who goes by the name Steve Smith started his cricketing career as a right-arm leg-spinning all-rounder but is now the best Test batsman of his generation.
"I had some tests done and then some further assessments deemed to be a mild concussion, so I've been ruled out of this Test match, unfortunately", he added.
"There will be times in the three Tests when England are in control, and we will be in control".
CA's head and trauma policy for 2019-20 was rolled out on July 1, without any major changes, and lists the use of neck guards as "recommended" but not mandatory.
Shane Warne suggested booing Smith in other instances was one thing but to add insult to injury was not on.
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Research carried out by Cricket Australia shows that delayed concussion - where symptoms don't develop until several hours after the initial blow - occur in approximately 30% of cases.
"You look at the game, only Steve developed a concussion".
A statement from the Australian Cricketers' Association on Sunday expressed disappointment in the reception Smith was given at various stages on day four.
"All that time while he was out there, there has been all this brain activity and a concussion going on and it is exactly why he should have rested in that time and not put himself back in immediate danger. To see the protocols practised at Lord's overnight was important and correct". Even today I was like "I know where I am, I'm good, I'm good, just get off the field" but there's a process now.
"With a pretty quick turnaround in between Test matches, I'm hopeful that I can make a recovery and be OK for that."
"I feel a little bit claustrophobic, I feel a little bit enclosed and not overly comfortable."
"I'm hopeful I'll be available for that Test match, but it's certainly up to the medical staff and we'll have conversations".