Singer Annie Lennox on Tuesday said she was "concerned for the safety" of fellow performer Sinead O'Connor after she posted a tearful video in which she said she was "fighting... to stay alive".
In the post, made in a New Jersey hotel on Thursday, O'Connor, 50, who has been diagnosed with bipolar disorder, said: "For the last two years, my entire life has been revolving just about not dying.
"I'm all by myself and there's absolutely nobody in my life except my doctor, my psychiatrist", who was the only thing "that keeps me alive".
"I'm fighting, fighting, fighting, fighting... to stay alive."
Former Eurythmics singer Lennox responded on Facebook, calling the video a "truly distressing call for help"
"She appears to be completely out on a limb and I'm concerned for her safety. Are there no close friends or family who could be with her to give her some loving support? It's terrible to see her in such a vulnerable state."
O'Connor is remembered for her arresting 1990 rendition of Prince's song "Nothing Compares 2 U", and its iconic video featuring the tearful and shaven-headed singer.
O'Connor quickly developed a name for inflammatory outbursts and caused an international controversy in 1992 when she tore up a picture of pope John Paul II on a US television show.
An unidentified poster on her Facebook account later wrote that the singer "is safe, and she is not suicidal."
"She is surrounded by love and receiving the best of care. She asked for this to be posted knowing you are concerned for her.
In recent years her posts on social media have become increasingly unfiltered, often threatening legal action against former associates, referring to physical and mental health difficulties and discussing troubles with her family and children.