Smith is hoping to bounce-back quickly.
Australia batsman Steve Smith has been ruled out of the rest of the second Ashes test against England at Lord's due to delayed concussion, Cricket Australia (CA) said on Sunday.
Smith was struck on the neck by a Jofra Archer bouncer during his innings on Saturday, forcing him to retire hurt, but he returned to the crease 40 minutes later and added 12 runs before being dismissed for 92.
"Steve Smith has been closely monitored by medical staff overnight," CA said in a statement. "He slept well but woke up with a bit of a headache and feeling of grogginess."
"As part of the CA concussion protocol, repeat testing was performed this morning and demonstrated some deterioration, which is consistent with the emergence of the symptoms he was reporting. On that basis, he has been withdrawn from the match."
Smith, who made 144 and 142 in Australia's first-test victory, did not field at the start of England's second innings on Saturday and will play no part in the last day of the match.
He was replaced by Marnus Labuschagne, who became the first concussion substitute in test history after cricket's governing body ICC included the rule in its playing conditions for international games from Aug. 1.
"With the tests that I've done and how I've woken up today I think it's the right decision. I'd love to be out there trying to keep performing to help Australia win another test," Smith, who will undergo a precautionary scan on Sunday, added.
Smith, who was also hit on the forearm during a hostile spell by Archer, will be assessed ahead of the third test in Leeds starting on Thursday.
"I'll be monitored closely over the next few days with a pretty quick turnaround in between test matches. I'm hopeful I can make a recovery," he said.
"But it's certainly up to the medical staff... it's an area of concern -- concussion -- and I want to be 100% fit."
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