It was on November 2 that Fox, spending time in his hometown Charlotte during Denver's bye week, was rushed to hospital for emergency open-heart surgery having collapsed on a golf course.
The 58-year-old, born with a congenital defective bicuspid aortic valve that he has known about for a decade and was putting off surgery on until after the season, missed four weeks of the campaign.
Denver rallied during and after the coach's return, though, and are now a game away from winning the Super Bowl as they prepare to tackle the Seattle Seahawks at the MetLife Stadium on Sunday.
In a joint press conference with opposite number Pete Carroll on Friday, Fox played down his health scare, saying: "I really never had any doubts (about coming back).
"They gave me a great projection of what the rehab was going to be like, how fast I could get back to normalcy - that is coaching for me.
"Really, it was like a sprained ankle. It was going to be four weeks. I was back to work on a Monday, four weeks post-op from open-heart surgery. I felt 150 percent better.
"I had a valve that was probably the opening the size of a pinhead. Now, it's a 50-cent piece. Just from a feeling good standpoint, I feel way, way, way better than I did two months ago."
Fox's remarkable 'sprained ankle' comment prompted a lighter moment as Carroll said: "What a stud. He's comparing an open-heart surgery and being on his back to an ankle sprain.
"Congratulations on that. That's really amazing. Come on John. That's awesome."
While there is palpable relief among the Broncos players now, the moment they found out about their coach's scare was a nervy time.
Star quarterback Peyton Manning said earlier this week: "Our first concern was for his health.
"'How serious was this? What was going to happen in the immediate future as far as potential surgery?'
"So really, the last thing we were thinking about was, 'When is he going to be back as our coach?"
They need not have worried, for Fox was soon involved in team planning again.
Manning added: "Maybe a week (after the surgery), we were in a team meeting and we had a big screen, and we had a FaceTime chat with Coach Fox.
"He didn't really know how to use it real well. He was very up close right into that camera, and I think it was his first FaceTime chat he had ever done ... (But) it was good for the team to see him. That was a special moment."
That special moment may pale in comparison to how it would feel if Fox can end a dramatic year hoisting the Lombardi Trophy, though.
"It is the pinnacle for everything that we do," said the coach. "There is only one happy camper in the end and that's going to be the team hoisting this trophy."