
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.
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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.