The 24-year-old Sunweb rider posted the eye-watering injury bulletin on Instagram, saying: "Fellas it's just as painful as you think it is."
"I had a small crash in training. I wish I could say I was doing something gnarly, but no, just on a bike path," he said.
"Nothing broken but since someone is going to ask what I did anyway, I ruptured a testicle."
In a sport where broken collarbones, wrists and ribs are par for the course, this is a rare injury and the unfortunate Hamilton did not know how long the recovery would be.
"It's a bit unknown, but at this stage all I can say is the surgery to do some repairs went well and I'll find out more in a follow up next week," he said.
"I am pretty devastated to be sidelined for the Aussie summer, but who knows, maybe a change will be for the best! See you all out on the road soon."
Hamilton finished sixth overall in the Tour Down Under last year and has ridden in the last two Giro d'Italias.