The Olympic long-jumper was ordered by doctors to not perform her tango with professional partner Ian Waite after damaging her knee during the final rehearsal.
Johnson and Waite were interviewed by Claudia Winkleman on the show and explained that the athlete's knee had "popped" during the finale of the routine.
"I heard a loud sound and straight away felt pain," she said. "I'm panicking a bit. Am I going to be able to start back training for my long jump in January?"
It is not known whether Johnson will return to the show next weekend.
Ex-cricketer Phil Tufnell and Katya Virshilas were voted off this week's show after losing out in the dance-off to Ricky Groves and Erin Boag.