Formula One champion Michael Schumacher is reported to have lost a quarter of his body weight since doctors put him in a coma to help him recover from brain injuries suffered in a skiing accident in December.

Schumacher's weight had dropped from 75kg to just 55kg in the 83 days since he was placed in a coma, according to reports in German media.

Schumacher, 45, suffered a serious head injury after striking a rock while skiing in the French resort of Meribel. He is being treated in Grenoble, where his family, including his wife Corinna, is maintaining a bedside vigil.