Young Australian opener Matt Renshaw will play no further part in the Sydney Cricket Ground test agaisnt Pakistan, after being diagnosed with concussion after two hits to the helmet.
Renshaw was hit on the grille when batting on Day One of the third 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.
However, Renshaw left the field during yesterday's final session, complaining of a headache.
The 20-year-old, who scored his maiden ton after recovering from Tuesday's bouncer blow, was withdrawn from the match by Brukner this morning.
"He rested in the dressing room [on Thursday]," said Brukner. "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.
"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.