Steve Smith's availability for the third Ashes Test is in doubt due to the concussion the Australia batsman suffered at Lord's.
England paceman Jofra Archer's vicious bouncer struck the former Australia captain on the neck.
Although Smith returned to resume his innings on Saturday, Cricket Australia (CA) announced the 30-year-old would not play any part on the final day of the second Test, when his team batted out a draw.
To understand why Smith's concussion may not have been spotted during initial assessments, Omnisport spoke to expert Dr Sam Barke, medical director of Return2Play, about the protocol and the measures typically taken.
Australia team doctor Richard Saw asked Smith a series of questions on the field including, "Where are we playing?" and "Who bowled the previous over?" What can the medical staff ascertain from this?
In the immediate aftermath you want to know how the player's feeling and then look at their orientation and memory, so asking those simple questions is just to see if they are responding correctly.
The doctor and physio will know the player and they can try and work out whether the player's responding correctly in a structured way.
CA said Smith "passed the CogSport and SCAT5 assessments" when he came off the pitch, so why was the concussion not spotted then?
The key to those tests is there is not really a pass-fail situation, it's just evidence building. Along with how the player is responding, how they're feeling and their symptoms, we do these tests to gather as much evidence as possible to try and work out whether the concussion has happened.
Unfortunately, there is not a 100 per cent test at the moment for concussion. It's adding all those pieces of evidence together to try and be as sure as we can.
Not infrequently we end up with situations like we had with Steve Smith where all the evidence from those tests has said, 'No, we don't think a concussion has happened'. Then further down the line symptoms start to come on.
Smith returned, misjudged a delivery and was given out lbw – later reviewing that decision when it clearly appeared he was out. Some people have said it was obvious from those acts that he was concussed - do you agree?
Being struck by a ball at that speed is quite a shocking incident that's going to be quite painful. Often people say, 'He clearly didn't look right'. But if you're in pain and you've had a shocking incident, you're not going to look right anyway.
That's not necessarily the same as concussion.
It was revealed today that Smith suffered a "delayed concussion response" – what is that?
The concussion itself hasn't been delayed. He had concussion from moment one. It's that he wasn't showing any signs or symptoms that concern that until now.
In my experience, the vast majority of time players do have some symptoms at the immediate point of injury and then they go away very, very quickly. It may have been by the time they got out there he was feeling absolutely fine.
So it looks like the Australia medical staff actually followed all the procedures correctly?
We reckon that probably about 10-to-20 per cent of concussions have that delay in onset.
As an outsider, it looks like everything's been done correctly and the right decisions have been made at every point, and he unfortunately fits into that small category of players that look fine at the time and then go on to develop symptoms further down the line.
CA said Smith is a "serious doubt" for the third Test, which begins on Thursday, and that per its concussion policy, he must not play or train until at least 24 hours after he has been cleared by the doctor. What is the process for a player returning to their sport and why do medics have to be careful?
You shouldn't be doing any activity until your symptoms have settled. In professional rugby they say you have to be 24 hours symptom-free before you start doing any sort of exercise. The theory is most people start to feel well when they do absolutely nothing and we want to see whether any symptoms come back with exertion and mental strain, so you gradually start to introduce exercise.
The big thing about concussion and the way you manage it, is the risk comes from further injury, not the initial injury. The risks from a one-off knock that's treated well are almost non-existent, but while the brain's still recovering, if it takes further knocks, that's when risks happen.
In the NFL, independent doctors are used to assess whether players have suffered a concussion. Do you think cricket should adopt a similar policy?
There's pros and cons to the argument. There are benefits of the medical staff knowing the players and being able to tell whether they are behaving differently. Independent doctors wouldn't know those nuances.
The vast majority of doctors make their calls that are in the best interests of an individual player rather than the team. They're more likely to be cautious than they ever have been.
I'm sure the team doctors are trying to make the right decision for the player and I doubt an independent doctor would have made a different decision in this case. The protocols seemed to have been followed correctly.
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