The veteran Warrington playmaker took two heavy blows to the head while carrying the ball into the Papua New Guinea defence 25 minutes into the match at Melbourne’s Rectangular Stadium.
But he played on after convincing medical staff that he was fit to continue.
However, Bennett said he was forced to bring Brown off at half-time after one of the non-playing members of his squad showed him a video of the incident towards the end of the first half.
Against his wishes, Brown was withdrawn from the action in the second half, with Josh Hodgson switching from hooker for the second half to help guide England to a 36-6 win that sets up a semi-final showdown with Tonga in Auckland next Saturday.
“The doctor who went on the field didn’t see the incident because there was no replay board,” Bennett said. “It wasn’t working.
“Kevin assured him he was fine. He had no major symptoms that suggested he’d been knocked out.
“Nearing half-time, one of our players who was not playing was on social media and up came a replay of the incident.
“He brought it in and showed the doctor and the doctor realised that (the injury) was a category one.
“Kevin was quite coherent in the changing room at half-time and the last thing he wanted to do was come off.
“But when you saw the replay you could see he was knocked out, it looked bad enough.”
Report: Page 5.