Steve Smith has been ruled out of the last day of the second Ashes Test between Australia and England due to a case of delayed concussion.
Smith was struck by a lethal bouncer from England pacer Jofra Archer on Saturday instantly causing him to fall to the ground face forward and crying in anguish.
After being forced to retire hurt as a result of the blow, Smith did return to bat later in the day and was dismissed for a vital contribution of 92 runs.
"Steve has been closely monitored by medical staff overnight and this morning reported that after sleeping well, he woke with 'a bit of a headache and a feeling of grogginess'," an Australian team spokesman informed.
Smith's injury is the first such instance under the new playing conditions introduced by the International Cricket Council which allows teams to have concussion substitutes for cricketers suffering a head or neck injury.
This substitute's role will not be limited to fielding and will bat or bowl if required.
Marnus Labuschagne becomes the first concussion substitute in Test history after his request was approved by the match referee and he will replace Smith in the remainder of the Test.
Labuschagne can now bat or bowl in Smith's place upon the discretion of his captain.
Meanwhile, doubts continue to linger over Smith's future participation in the series with the 30-year-old unlikely to get fit in time for the third game starting on Thursday.
Smith has thus far been Australia's batting mainstay with scores of 144, 142 and 92 in the three innings his team has batted.
The spokesman declared Smith's left arm, which was also subject to a spray of short deliveries by Archer, was much better and not a cause for concern.
The spokesman admitted Smith was suffering from delayed onset of his concussion since he had been showing the relevant symptoms all morning.
"On that basis Steve has been withdrawn from the match by team doctor Richard Saw," the spokesman said.
In light of permitting Smith to resume his innings late on Saturday, he added: "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.
"Steve's fitness will be assessed on an ongoing basis.
"Steve will undergo a precautionary scan on his neck on Sunday."