Australia will be without batsman Steve Smith for the third Ashes test against England because of a concussion.

On the fourth day of the second test on Saturday, Smith had to leave the field after being hit on the neck by a fast, sharply rising delivery from Jofra Archer.

Tests were conducted before Smith was allowed to return to complete his innings. Smith complained of headaches later Saturday and was ruled out of the remainder of the match after displaying concussion symptoms.

Australia coach Justin Langer says Smith "felt a bit better yesterday but he is not going to have time enough to tick off everything he needs to do to be ready to play."

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"He was probably a couple of days off being fit," Langer said.

"It was really a no-brainer.

"Like all players, he wants to play — but he understands as well he's not 100 per cent yet." Langer likened Smith's omission to England paceman Jimmy Anderson's calf injury but backed his charges to "fill what is almost unfillable shoes".

Australia leads the series 1-0.