The Australian opener Matt Renshaw has pulled out of the remainder of the third Test against Pakistan in Sydney, after being been diagnosed with concussion after two hits to the helmet.
Renshaw was hit on the grille when batting on day one of the Test, then struck on the top of the helmet while fielding at short leg on day three.
On both occasions, team doctor Peter Brukner assessed Renshaw and gave him the OK to stay on the field.
But Renshaw left the field during Thursday's final session complaining of a headache.
Brukner said they have been regularly checking the player.
"He rested in the dressing room (on Thursday) and then, when we returned to the hotel, we performed concussion tests and his cognitive, balance, co-ordination and reaction times were all within normal limits," Brukner said.
"However, on Friday morning he was still symptomatic and so we have taken the decision to withdraw him from the match as he is suffering from concussion.
"We will continue to monitor him over the coming days and work with him to produce a gradual return to play."
Meanwhile, Matthew Wade has recovered from a stomach bug and is expected to take the gloves on Friday after Peter Handscomb filled in on Thursday.
Rain has delayed Friday's start of play.