Celine Dion was diagnosed with the incurable Stiff Person Syndrome last year and has been unable to perform.
Her sister Claudette shared a heartbreaking update on her illness.
Claudette shared that Celine no longer has control over her muscles as she battles the condition.
"She's working hard, but she doesn't have control over her muscles," she explained.
She has been unable to perform with her diagnosis
PA
"What breaks my heart is that she's always been disciplined. She's always worked hard."
Celine has previously revealed muscle spasms were affecting her "daily life" and creating problems with her mobility and vocal cords.
Her vocal cords could continue to be affected as her muscles suffer.
"The vocal cords are muscles, and the heart is also a muscle," Claudette told 7 Jours.
"This is what comes to get me. Because it's one out of a million cases, the scientists haven't done that much research because it didn't affect that many people."
Claudette added it is likely to be a while before the Canadian pop legend returns to the stage, but it is still something she hopes to do.
The singer's sister added she doesn't know in "what capacity" Celine would be able to do this, however.
Celine, 55, has mostly stayed out of the public eye since her diagnosis.
LATEST DEVELOPMENTS
Celine's sister shared an update on her condition
PA
What is Stiff Person Syndrome?
Stiff Person Syndrome is a rare disorder that has various treatments available, but none that can cure it.
The body attacks itself as the immune system targets healthy cells.
More research is needed to find out why people develop the illness.
It causes muscle stiffness throughout the body and can cause spasms over time.