Steve Smith has spoken after being pulled out of the second Ashes Test with concussion following a sickening blow to the neck while England captain Joe Root also reacted to the shocking developments.
Australia will head to Leeds for the third Test on Thursday needing just one win from the remaining three matches to retain the Ashes.
That was the reward for gritty day five batting by Marnus Labuschagne (59) and Travis Head (42 not out) as the visitors finished 6/154. England had hopes of levelling the series after Ben Stokes (115 not out) helped set up a declaration of 5/258, creating a lead of 266 with 48 overs to take 10 wickets. Australia was in some trouble at 3/47 after the top order failed again but the Labuschagne and Head steadied the ship.
On day four, Smith was struck by a Jofra Archer bouncer that sent him crumbling face first to the turf before he was taken off the ground and assessed for concussion symptoms.
He was given the all-clear by Australia's medical staff to return to action and resumed his innings before being dismissed LBW for 92.
Speaking after the Test ended in a draw, Root said he was amazed to see Smith again after his nasty knock.
"I couldn't believe that he managed to come back out and play," Root said. "He was obviously desperate to do well for Australia and his teammates.
"All of us in the dressing room just want to wish him a speedy recovery. It's not a nice moment, you never want to see someone go down hurt."
Although he was deemed healthy enough to bat again, Smith didn't field in the final session on day four and he was officially withdrawn from the match on day five after he underwent further concussion testing — the results of which had deteriorated from his initial tests.
Australia lodged an application to use a concussion substitute and the ICC match referee granted the request, allowing Labuchagne to join the contest.
The young Queenslander fielded in Smith's place before replacing him at number four in the order, making it the first time in Test cricket a concussion sub has ever been used.
Smith said he felt fine on day four and was comfortable to keep batting but agreed the right decision had been made to withdraw him after he felt a bit ill the morning after he was hit.
He also said he's hopeful of being declared fit to play the third Test starting in Leeds on Thursday but knows there's still plenty of boxes he needs to tick beforehand.
"I started to feel a little bit of a headache coming on probably as the adrenaline got out of my system," Smith said. "I woke up feeling a little bit groggy and with a headache again.
"I didn't actually have any real pain in my neck yesterday when I touched it or when anyone else touched it. Today I do have a bit of pain there, whether that's some swelling or what, I'm not sure. Perhaps that's leading to me having a headache and feeling a bit groggy.
"It's obviously a quick turnaround between Test matches. I'm going to be assessed over the next five or six days, each day a couple of times a day, to see how I'm feeling and how I'm progressing. 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.
"It's certainly an area of concern, concussion, and I want to be 100 per cent fit.
"I've got to be able to train a couple of days out and then face fast bowling to make sure my reaction time is in place. There's a few tests I'll have to tick off and time will tell."
Smith doesn't wear the stem guards on his helmet that were introduced to protect the neck in the wake of Phillip Hughes' tragic death because he finds them uncomfortable but revealed he may need to look at using them in future.
"I think I, along with a few other players in the team, find it a little bit different, uncomfortable compared to what we're used to," he said. "I feel a little bit claustrophobic when it's on.
"I feel like I'm enclosed and not overly comfortable. It's certainly something I need to probably have a look at and perhaps try in the nets and see if I can find a way to get comfortable with it."
Smith was monitored by medical staff overnight and fresh tests on the morning of day five convinced the team doctor he should take no further part in the match.
"As part of the Cricket Australia concussion protocol, repeat concussion testing of Steve Smith was also performed this morning and demonstrated some deterioration from his testing which is consistent with the emergence of the symptoms he was reporting," a Cricket Australia spokesman said.
"On that basis Steve has been withdrawn from the match by team doctor Richard Saw."
Smith will undergo a precautionary scan on his neck today.
Cricket Australia said it was "proud" to have led the way in implementing guidelines — which have been used already in domestic cricket Down Under — to cater for an instance such as this.
"Despite the unfortunate nature of what has happened, the positive is that the concussion protocol, including the availability of the concussion substitute, which has recently been brought in has served its purpose," CA said.
"A player is no longer under pressure to take the field when he or she displays symptoms of concussion and a side is not disadvantaged having lost a player to a blow to the head or neck.
"Cricket Australia is proud to have been leaders in this area, having introduced concussion substitutes in domestic cricket and worked with the ICC to introduce them in international cricket."
Cricket Australia's concussion and head trauma policy does not dictate Smith must sit out a specific period of time beyond the initial 24 hours but the decision to let Smith bat on day four after being hit will be heavily scrutinised.
Smith passed all his tests on Saturday. However, it is not unusual for concussion symptoms to appear 24-48 hours after a head knock.
Coach Justin Langer, who famously wanted to bat in a Test against South Africa in 2006 despite being hospitalised with concussion, defended the call to let Smith bat.
"These are like my sons alright, so you're never going to put them in harm's way," Langer said after day four.
"I was saying, 'Mate, are you sure you're OK?' … I asked him behind closed doors two or three times. I asked him in front of the group.
"He just kept going, 'All good, all good coach. I'm ready … I can't get up on the honour board unless I'm out (there) batting'. What else do you do? The medicos cleared him."
During his innings of 92 but before he was felled by the ball to the neck, Smith copped a nasty blow to his left forearm that stopped play for a lengthy amount of time as he was assessed by team medicos.
Langer said after stumps on day four Smith was actually more concerned about his arm and being able to grip the bat properly than he was about any concussion fears.
X-rays on day four cleared Smith of any fracture and on day five he said his arm was feeling much better.