The Lady Marmalade star is due to perform with professional partner Artem Chigvintsev on Monday night's (23Mar15) live show, but in behind-the-scenes footage from Sunday (22Mar15), the singer reveals she is struggling with pain in her leg.
In the video, obtained by Eonline.com, she admits, "It feels like it's broken. I woke up with it this morning killing me."
LaBelle, 70, is set to perform a dance to her favourite song, 50 Cent's In Da Club, on Monday and although she is nervous about hitting the dancefloor with her bad knee, she says, "I'm scared but this is my song. Nothing's gonna stop Patti but Patti...! Whenever I hear the song, it makes me happy."
Other contestants on season 20 of the hit show include LMFAO's Redfoo and actors Rumer Willis, Suzanne Somers, Willow Shields and Riker Lynch.