Australia's Steve Smith has been ruled out of the last day of the second Ashes Test with concussion against England at Lord's, saying he felt "groggy" on Sunday morning.
Smith was felled when a Jofra Archer bouncer struck his neck on Saturday.
"I started to feel a little bit of a headache coming on last night as the adrenaline got out of my system but I was able to get a good night's sleep in, but I woke up feeling a bit groggy and with a headache again," Smith said.
"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."
The series is the first being played under the International Cricket Council's new concussion substitute regulations, part of the inaugural World Test Championship.
These allow players who have suffered head or neck injuries to be replaced fully by a substitute, who was previously restricted to fielding alone.
Marnus Labuschagne, on the field as 12th man when play resumed Sunday, became the first concussion substitute in Test history after Australia's request was approved by match referee Ranjan Madugalle.
There are doubts whether star batsman Smith will feature in the third Test at Headingley starting on Thursday, with an Australia team spokesman saying "the short turnaround is not in his favour".
Smith was hit by an Archer bouncer when on 80 on Saturday and retired hurt.
He resumed his innings at the fall of the next wicket after 46 minutes off the field, and was eventually out for 92 -- the first time this series he had been dismissed for fewer than 100 runs.
Cricket Australia statistics show that 30 percent of concussions in Australian cricket are delayed.
- 'Right decision' -
But the Australia spokesman defended the decision to let Smith resume batting by saying: "It is not uncommon for players to pass their tests and feel well on the day of an injury and then display symptoms 24-48 hours later."
Smith had no qualms about being withdrawn from the match, saying: "I think the right decision has been made."
Significantly, Smith was wearing a helmet without the additional stem guard neck protection introduced following the death of Phillip Hughes after his former Australia team-mate was hit by a bouncer in a 2014 domestic Sheffield Shield match in Sydney.
"I, along with a few of the other players in the team, find it a little bit uncomfortable, I feel a bit claustrophobic and a bit uncomfortable," said Smith.
"But it's something I need to have a look at and try in the nets to get comfortable with it," he added.
As for his prospects of playing in the third Test, Smith said: "Obviously, there's a quick turnaround between Tests.
"I'm going to be assessed each day, hopefully I will be available, but it's certainly up to the medical staff.
"It's certainly an area of concern, concussion, and I want to be 100 percent fit. There's obviously a few tests I have to tick off and time will tell."
Both sides could be without their star players at Headingley if Smith is sidelined given James Anderson, England's all-time leading Test wicket-taker, broke down after bowling just four overs at Edgbaston with a calf injury that ruled him out of the second Test.
Australia, bidding for their first Ashes campaign triumph on English soil in 18 years, lead the five-match series 1-0 after a 251-run win at Edgbaston last week.
In that match, former captain Smith marked his first Test since completing a 12-month ban for his role in a ball-tampering scandal in South Africa with superb innings of 144 and 142.