The 37-year-old New Zealander revealed after Saturday’s 22-20 Grand Final win over Wigan that he had been suffering from a heart condition.
“That was a really difficult moment, a really scary moment for Kylie, first and foremost,” McDermott told BBC Radio Leeds. “The players’ health is paramount.
“Kylie just wanted to play and we were saying ‘you’ve got to get this looked at’.
“We went through something similar with Ben Jones-Bishop who had a blood condition and simply wasn’t getting enough oxygen around his body. We missed him for a fair chunk of time. Kylie was staring down the barrel of something similar.
“One of the options was to take a short-term medication that would settle his heart down and give him more of a regular heartbeat but it was not going to be fixed and, if he was to push himself, like players do on the field, past the point of fatigue, who knows?
“But that was Kylie’s decision, he cracked on. He was limited in what he could do but while he was on there, he was very very effective.
“Kylie has probably not been known for his 30-minute spells, he was always a 15-to-20-minute man but, by his own admission, after 10 minutes he was done.
“So his task was to go on the field and create as much havoc as he could for 10 minutes and I’ve got to say it worked. He was a piece in the jigsaw that worked.
“Players talk about putting their bodies on the line, well I don’t think it’s being over-dramatic to say Kylie was putting his life on the line for the group for the final 15 rounds of the season.”