Linda Ronstadt is suffering from Parkinson's disease and says she can no longer "sing a note".
In an interview with the retirees' organisation AARP, to be published next week, Ronstadt, 67, said the diagnosis she received eight months ago had answered the question of why she had become unable to sing.
"No one can sing with Parkinson's disease," she is quoted as saying in her interview with the lobbying group for older Americans. "No matter how hard you try."
AARP said she had to walk with sticks on uneven ground and used a wheelchair when travelling.
"Parkinson's is very hard to diagnose, so when I finally went to a neurologist and he said, 'Oh, you have Parkinson's disease', I was completely shocked. I wouldn't have suspected that in a million, billion years," she said in the interview.
Ronstadt has won nearly a dozen Grammy awards and sold more than 100 million albums worldwide, according to Simon & Schuster, which is due to publish her memoir this year.
The Arizona-born singer's 1974 record Heart Like a Wheel yielded hits including You're No Good, When Will I Be Loved and It Doesn't Matter Anymore.
The soft rock album soared to No. 1, selling more than 2 million copies.