In a series of tweets, Lady Gaga announced that she will once again have to cancel a concert due to health issues.
Gaga posted a photo of her "Rio" tattoo on Instagram captioned with an apology to the Brazilian city.
The singer has been hospitalised days after revealing she suffers from chronic pain condition Fibromyalgia, and now she has pulled out of her South American festival gig on Friday.
In the first trailer for her documentary, titled "Five Foot Two", the pop star was seen at a doctor's office, and at the Toronto Film Festival, spoke further about how the film explores her struggle.
Rock in Rio, which starts Friday, is to feature Maroon 5, Fergie, Aerosmith, Bon Jovi, Red Hot Chili Peppers and Guns N' Roses.
Fibromyalgia causes musculoskeletal pain throughout the body.
"I ask for your grace and understanding, and promise that I will come back and perform for you soon".
"Remember years ago when I tattooed Rio on my neck, the tattoo was written by children in the favelas. Rio".
Fibromyalgia is characterized by pain that radiates throughout the body, especially in the muscles and joints. The disease affects an estimated five million in the United States, a lot of them women. Often, it is accompanied by severe sleep disorders and intense fatigue. I love you so much. I'm hospitalized, " she said. You occupy a special place in my heart.
The singer of hits like "Million Reasons" and "Perfect Illusion" had been due in Rio as part of her Joanne World Tour, which ends in December.
Gaga added that she believed music had the power to help those who are suffering. But now, uncertainty hangs over the rest of the tour.