The 33-year-old developed a severe complication from a bacterial infection
British television sports presenter Charlie Webster is in a coma at a Rio hospital after contracting a rare strain of malaria.
The former Sky Sports News presenter fell seriously ill after completing a 3,000-mile charity cycle from London.
She was admitted to hospital on 6 August after watching the Olympic opening ceremony, having arrived in Rio a few days earlier.
Initially doctors thought she was dehydrated following the gruelling six-week Ride to Rio challenge.
But her condition deteriorated after developing a severe complication from a bacterial infection.
However, there was a fresh tweet on her Twitter account just after 9.00am on Thursday, thanking well-wishers for their "messages of support".
The 33-year-old had tweeted the day after being admitted to hospital: "6 weeks on the road ends in this. Very rough day, severe dehydration & infection - 2 drips & antibiotics #Rio."
Just two days later she wrote: "I'm getting there...awful few days with serious infection #Rio."
Webster made no more posts and a statement on her Facebook and Twitter profiles on August 11th revealed how her condition had worsened.
A message about Charlie: pic.twitter.com/dKb89bWr83— Charlie Webster (@CharlieCW) August 11, 2016
It said: "Charlie has updated you all throughout her cycle and we know her silence was causing concern."
"On Saturday, 6th August, Charlie became unwell and was admitted to hospital in Rio de Janeiro."
"What was initially thought as dehydration, caused by her riding to Rio, has since been diagnosed as a severe complication caused by a bacterial infection."
"Charlie is receiving great care and we will update when we can."
The Ride to Rio campaign wished Webster a speedy recovery, describing her as a "tough lady".
A UK Foreign Office spokesman said: "We are providing support to a British woman who is in hospital in Rio."