The 'Fight for this Love' singer has turned yellow from jaundice, is still on oxygen, and was hours from death following her infection with the disease – believed to have been caused by a mosquito bite while she was holidaying in Tanzania with her rumoured boyfriend Derek Hough.
A source told the News of the World: "We nearly lost her and the battle is far from over. She is so weak and this horrible illness has taken complete hold of her.
"It got so bad she was literally only hours from death's door. Thank goodness she was diagnosed in time.
"Even now she can't talk. She drifts in and out of consciousness and when she comes round all she can do is sob.
"There was no news coming out of the hospital because it was all so touch and go. We couldn't give any assurances to fans because there weren't any to give."
The insider added she was still in a "very serious" state despite leaving the London's University College Hospital late last week to be treated in a private clinic.
The source said: "Seeing Cheryl like this is so painful. She could easily have dead. And she's not better, she's not even close. It's still a very serious situation and she's really going to have to
battle."
It is also not thought she will be able to return to UK TV talent show 'The X Factor' for a while, putting the live shows – which begin in late September – in jeopardy.
The source added: "Cheryl's not going to be back for a long time. She won't be seen in public for at least two months. This is a big wake-up call. She can't go on as before or she'll push herself to the brink
again."