The TV host, who was working with the Team GB Olympic media team, is in an induced coma in a Rio hospital with a rare strain of the disease.
It's thought that Charlie, a former Sky Sports presenter, contracted the illness during a charity bike ride to Rio from London's Olympic Stadium. After cycling the 3,000 miles she was due to stay on in Rio as part of Team GB's Great Britons campaign, alongside Nick Grimshaw and Jodie Kidd, but fell ill shortly after the opening ceremony.
Initially thinking she was suffering from dehydration, Charlie and her family, who have travelled to the hospital in Rio to be by her side, have since discovered she's contracted a rare form of malaria.
Tweeting her fans when she first fell ill, Charlie shared two pictures of herself in the hospital. In the first, the star can be seen hooked up to a drip with the caption: '6 weeks on the road ends in this. Very rough day, severe dehydration & infection - 2 drips & antibiotics #Rio'
In the second, Charlie is laying down in her hospital bed: 'I'm getting there...awful few days with serious infection #Rio'
Her condition has since deteriorated, and the 33 year old is now in an induced coma. A source close to the star has said: 'Charlie is battling for survival at the moment – everyone is distraught.
'But she is so strong and a very fit and healthy person in general so we have to keep positive.'
Charlie with her ex-boyfriend, Downton Abbey star Allen Leech
Charlie's mother, brother and manager have flown from the UK to be by her side. Taking to her Twitter account to share an update with concerned fans, a post on behalf of the star reads: '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.'
A message about Charlie: pic.twitter.com/dKb89bWr83— Charlie Webster (@CharlieCW) August 11, 2016
Wishing you a speedy and full recovery, Charlie.