The singer was working out with a weighted fitness ball in a gym and she suffered a painful injury when it struck her in the face.
Roberts tells U.K. Tv show Good Morning Britain, "It was like one of those YouTube videos you watch of people knocking themselves out in the gym. That was me! I picked up a medicine ball... chucked it at this trampoline and it came back with a vengeance. It just knocked me out. Black eye, swollen nose, swollen lip..."
However, Roberts had no time to dwell on her injuries because she was due to perform a skit with British presenting duo Ant MCPartlin and Declan Donnelly that evening as part of their touring comedy show.
She adds, "My manager's actually a boxer so he put a silver spoon in ice and rubbed it for about 3 hours before the show. I looked a little bit like I'd gotten some work done... Thank God for make-up and a good make-up artist. I wore my hair a bit in my face so nobody really knew... it was kind of rough to get through the next couple of shows but the show must go on."
The comedy tour concludes on 7 September (14) in Newcastle, England.