Mary Lou Retton -- an Olympic gold-winning gymnast -- is currently fighting for her life in the ICU ... this according to her daughter, who says her mom is battling a rare form of pneumonia.
McKenna Kelley shared the sad news on Tuesday via her Instagram story with a photo of a SpotFund account that she started for Retton's medical costs.
"Please help my mom continue to fight," Kelley said in the post.
The fundraiser says the 55-year-old former athlete is unable to breathe on her own due to the rare form of pneumonia.