(CNN) -- Endurance swimmer Diana Nyad was stung by a sea creature for a second time Saturday night and was being treated by doctors, her team said in a blog post, leaving the continuation of her swim in question.
The 62-year-old, in transit from Havana to Florida, was stung by some kind of presumed jellyfish, the blog said.
"Her face and eyes and the area around her eyes are affected. She is out of the water and aboard the transom of the Voyager where she is being treated by doctors. It will be up to Diana to decide whether or not to continue to the swim."
The incident was another setback for the athlete, who was stung by Portuguese man o' war earlier in the day.
At 6:30 p.m., Nyad was 49 miles from Havana.
Having passed the 24-hour mark, she was entering a critical time in her quest to cover the 103 miles.
"Tonight, her second night in the open water, may be the most critical," the team wrote. "Steve Munatones, the independent observer for the International Swim Federation who is accompanying the expedition, says that swimmers have a much better chance of success if they can make it through the second night."
There was a bit of excitement early Saturday afternoon. An oceanic whitetip shark swam near Nyad, but a diver on her team faced it off and it meandered away.
The swimmer improved her performance late Saturday morning after struggling to maintain her usual stroke rate, her support team said. Fortified by chicken soup, Nyad was making good progress until the Saturday evening incident.
"This afternoon -- it is stunning to actually witness -- Diana is swimming stronger and stronger," one post said. "Her strokes are up to 50 per minute, she is eating pasta, gobbling bananas, bits of peanut butter sandwiches, along with high-carb & high calorie liquid concoctions."
The going was rough before dawn Saturday, when Nyad had stopped her freestyle stroke and complained that she couldn't breathe properly after getting stung.
Doctors from the University of Miami gave the swimmer a shot to reduce inflammation, oxygen and other medication, the blog said, and after treading water for an hour Nyad said she felt better.
Candace Hogan, a friend who has been on most of Nyad's swims since 1978, said she could recover and complete the 100-plus mile marathon, the blog said.
The team initially said Nyad had likely been stung by a moon jellyfish but revised that to say it was the more troublesome Portuguese man o' war.
A National Institutes of Health report says an encounter with a Portuguese man o' war can lead to "significant systemic reactions" but rarely death. While mild stings generally produce localized pain, severe ones can provoke symptoms ranging from headaches to seizures, delirium, coma and paralysis, as well as breathing problems, cramping and vomiting, the NIH says.
Chief handler Bonnie Stoll said on Twitter that Nyad had been "stung along both arms the side of her body and her face."
Nyad had to clear herself of tentacles, change her swimsuit and put on a shirt for protection after the incident.
Another member of Nyad's support team said the way she handled the setback was a "testament to her strength."
"It was scary," Stoll said. "But Diana is happy that this happened early while she is still at her strongest."
A safety diver who entered the water to help Nyad was also stung numerous times, her blog said. He received treatment back on one of the flotilla of boats accompanying her.
Nyad began her swim just after 6 p.m. Friday from Havana's Hemingway Marina.
The former world champion swimmer expects the swim to take close to 60 hours, which would put her into Florida sometime Monday.
Nyad last attempted this swim in early August and had to be pulled from the water after some 60 miles, and almost 29 hours of swimming. She blamed a shoulder injury she suffered early in the journey, and an 11-hour-long asthma attack.
Her first Cuba-Florida attempt, back in 1978, was brought to an end by strong currents and bad weather after almost 42 hours in the water, according to her website.
CNN's Matt Sloane and Shasta Darlington contributed to this report.