Mark Ballas sat out Monday's performance for "Dancing with the Stars" after suffering a back injury during last Sunday's rehearsals. According to sources close to the show, it is not yet clear if the choreographer, dancer, musician and actor will be able to return this week or for the rest of the season.

As reported by People, Ballas and his dance partner Paige VanZant, a strawweight fighter for the UFC, were practicing their routine and camera-blocking movements on Sunday when the former stopped the rehearsals due to pain in his back.

In a video obtained by the news site, Ballas can be seen walking away from his partner before lying on the floor and wriggling from the pain.

"I just slipped a disc," Ballas can be heard saying in the clip. "My back pinched funny. I'm hurting. Oh yeah, I'm in trouble."

According to VanZant, Ballas was planning on incorporating a few fancy tricks into their routine during the rehearsals. However, since they didn't have time to warm up that day, she suggested skipping the tricks.

"We weren't warmed up, so I wasn't going to do the tricks," VanZant said. "But he said we had to because we didn't have a lot of time. We'd done the first trick 100 times. But the first time we did Sunday, he hurts his back."

As reported by International Business Times, Ballas aggravated an old injury during the rehearsals. He's scheduled to undergo an MRI and CT scan later this week, but it is not yet clear when he will be back.

"Mark is recovering, but we are not sure what is happening moving forward," VanZant said. "We don't know how hurt he is, but we're hoping for the best."

Due to Ballas' injury, VanZant went on with Monday's performance without her dance partner. Instead, Alan Bersten, a former contestant and now a member of the show's dance troupe stepped in as the UFC fighter's partner.

"I feel horrible that Mark is hurting, but stepping in for him has been a dream come true," Bersten said. "But at the end of the day, it's all about Paige. I'm just happy I was there to support her tonight."