Jo Sung Mo,had fractured his ankle

According to Jo Sung Mo's representative, "They were doing a long jump segment at the military academy when Jo Sung Mo landed awkwardly and jarred his left ankle. He was immediately sent to a hospital for treatment as filming was suspended temporarily. After initial diagnosis by the doctors, it was decided that an emergency operation had to be done. It's still early to determine when will Jo Sung Mo return to the show."

But with ankle injuries taking a while to heal and the show being more towards the sports side, it's hard to see Jo Sung Mo coming back in the short term.