Davina McCall is undergoing medical tests after fears she may be suffering from hypothermia after battling severe weather in a Sport Relief challenge.
The presenter attempting to travel 500 miles under her own steam as she heads from Edinburgh to London by running, swimming and cycling.
But McCall, 46, has been struggling with the elements after beginning the seven-day journey on Saturday, putting her health at risk.
Sport Relief chiefs said today that she is "undergoing a medical assessment after suffering suspected signs of hypothermia".
So far in the BT Sport Relief Challenge: Davina - Beyond Breaking Point, she has pedalled her way through temperatures which have been just 3C (37.4F), plus a further chill from winds of up to 40mph. She was due to complete a 14-hour, 130-mile cycle to Keswick today.
Professor Greg Whyte, the trainer for the Sport Relief challenges, said: "These are the worst weather conditions we've seen on any challenge - it's the worst weather ever."
It is the latest health setback during a Sport Relief challenge. In previous years David Walliams picked up bugs during swimming down the River Thames, as well as developing sores from his wetsuit, and two years ago John Bishop was left in agony amid worries about stress fractures as he did back-to-back marathon distances while travelling from Paris to London.