Navratilova, 54, was diagnosed with high-altitude pulmonary edema, which is a collection of fluid in the lung. She was helped down the mountain in Tanzania and taken to a hospital in Kenya for treatment.
"It is potentially dangerous when someone is at high altitude, but once brought down, recovery is quick," said Dr. David Silverstein, who treated Navratilova at Nairobi Hospital. "Martina is doing well and will continue to do well."
Navratilova was among 28 people with the Laureus Sport for Good Foundation climbing the 19,340-foot Mount Kilimanjaro.
"I'm disappointed not to be able to complete this amazing journey," Navratilova said on a blog about the climb. "It was something that I have wanted to do for so long but it was not to be.
"I am so pleased that we got it going and I will be watching and waiting for news from the climb when they reach the summit (Saturday). I didn't make it but I think it has been a great success as we have raised funds and awareness for the work that Laureus does."
Navratilova compiled a 1,442-219 singles record in her career and had nine Wimbledon championships among her 167 singles titles. In addition to 18 major singles titles, she won 31 major doubles championships.