Australian batsman Steve Smith was forced off the field during the second Ashes Test after being struck by a 92.4mph delivery.
The ball from English paceman Jofra Archer hit Smith on his neck when he was on 80 not out.
Smith immediately hit the ground and remained there for an extended period before stumbling to his feet.
After being examined by team doctors, the 30-year-old was persuaded to leave the field, despite his reluctance.
He left his side on 203 for six, 55 behind England on the fourth afternoon of the Test.
Smith returned 40 minutes later after Peter Siddle fell to Chris Woakes, hitting his first two balls for four.
He eventually fell LBW to Woakes for 92.
By tea on Saturday, England had bowled out Australia for 250.
A statement from Cricket Australia said: “Steve was hit on the neck below the left ear.
“He was assessed lying on the pitch at the instructions of team doctor Richard Saw.
“Dr Saw made the precautionary decision to remove Steve from the field of play to have him further assessed under Cricket Australia’s head impact protocol.
“Steve then passed his assessments and will now be monitored on an ongoing basis, as is routine.”
Archer had been bowling at speeds of up to 96mph (154 kph) in what was reportedly the fastest bowling seen from an English bowler in a generation.
One of his earlier balls had struck Smith on the forearm.
Smith scored two centuries during the first Test, helping his side to victory over the English.