Aleksandar Mitrovic apologised to Newcastle United's doctor after the Tyne-Wear derby.
Mitrovic netted a dramatic late equaliser for the club in Sunday's 1-1 draw at St James's Park.
The striker went on to suffer a head injury after a clash of heads with Sunderland's Lamine Kone.
Mitrovic was unconscious for a few seconds, but wanted to continue for the final few minutes of injury time.
However, club doctor Paul Catterson, following Premier League protocol for concussion, told manager Rafa Benitez that Mitrovic should not be allowed to continue.
And the 21-year-old had to be physically stopped from attempting to get back on to the pitch by Benitez and Catterson.
Speaking in his native Serbia, Mitrovic said: “I didn’t know what the procedure was.
"I didn’t know the rules. I apologised to the doctor after the game, because I knew I had to come off after being knocked unconscious for a few seconds.
"I’ve been through the examinations, my head is fine.”
Catterson – who was widely praised for his actions in the derby – has spent the past seven years at St James's Park.