"I'm just a keen sportsperson looking for a challenge in a different sport," Watson says.
"Will I be terrified on the night? Hell yes.
"But I want to front up. I need to push myself in something. It's really about me versus me."
He has been guaranteed it won't be promoted as a grudge match.
"I have no personal issue with Jesse and have been guaranteed it will not be promoted as a grudge match.
"I thought hard about this but concluded it's easy for talkshow hosts to be accused of hiding behind the mike."
Watson, who formerly ran Triathlon New Zealand's European base, for several years, is renowned for hard-hitting opinions.
In the past he has accused New Zealand cricketers, including Ryder, of failing to meet the standards of physical fitness required at elite level in other sports.