The next day Betham continued training on the heavy bag, but, "I didn't feel good. My head was sensitive and I was a little sensitive to light but nothing to associate it with concussion. Even when I hit the bag I could feel something in my head. I didn't feel right so I rang my doc".
Hanna advised him to get a concussion test from regular physio Jonathan Moyle, which Betham passed. But soon afterwards the serious problems began.
"Progressively, my body started stiffening up - my hamstrings, my glutes and through my back - to the point where I couldn't even get out of bed," he said. "Even turning over in bed was extremely painful.
"It was frightening. I have a high pain threshold but ... it felt like someone was stabbing me every time I moved, that's how bad it was.
"I had a brain bleed or head bleed, and the fluid leaked down the spine into the lumber area which just crippled me. The scary thing is if that hadn't happened, I would have fought because I had passed the concussion test. I would have fought a 10-round fight with a brain bleed. I could have been history."
The diagnosis was made after an MRI scan, which took almost two hours, following which Betham was told: "You're going to hospital straight away, but you can't drive - you need your wife to pick you up and take you."
Betham spent the night under observation at Auckland City Hospital. After he was sent home and the symptoms cleared, the Sky Television presenter travelled to Rio to cover the Olympics, all the while wondering about his boxing career.
I had a brain bleed or head bleed, and the fluid leaked down the spine into the lumber area which crippled me.
Late last week he came to his decision. The former New Zealand Warriors captain, who played nine tests for the Kiwis and played at the 2000 World Cup for Toa Samoa, is a professional sportsman no more.
When the Herald called at his Greenlane home there is boxing showing on the television, but Betham knows he can no longer be a fighter.
"It's hard," he said. "At the time when I was going through it, it was easy. I told my wife, Jaymie, 'I'm done. Don't worry about it'. But then as it went on, I went back to the gym and it cleared up, for that brief moment when I was told 'you're clear', I wondered 'can I fight?' I got a spring in my step again because there were a few more things I wanted to do. And then I thought 'just one more fight'. But then I thought 'that's what they all say, and if this happened in sparring with 16oz gloves and headgear, what it's going to be like with 10oz gloves?'
"You can't gamble like that. I tell a lot of people, 'if you think about what's important in life, there's nothing more important than family'.
"I am so grateful to all the medical staff who have helped me, and in particular Chris and Jonathan, and all my supporters everywhere."
Betham's father, Monty Senior, fought 53 bouts as a professional at both middleweight and light heavyweight, with 43 victories.
Among his son's fighting highlights are beginning his professional career in Samoa, his father's birthplace, winning the New Zealand cruiserweight title, and losing to Shane Cameron by decision, the only loss of his nine-fight pro career.
"Winning a New Zealand title was great, but I never felt as good as I did in that loss," he said. "I felt amazing. Shane was world-ranked at that stage and I took the fight on two weeks' notice. My trainer Lolo Heimuli was incredible. Shane is a hero of mine, and he was in a tough position too - he couldn't win either way - but he didn't knock me out."
