Sabine Kehm issued a written statement saying Schumacher's condition "remains critical but stable."
"We would like to clearly stress that any information regarding Michael's health not coming from the doctors treating him or from his management must be treated as invalid and pure speculation," the statement said.
Schumacher, who turned 45 Friday, suffered a serious head injury in a fall at the French resort of Meribel Dec. 28, and has been in a medically induced coma in Grenoble.
The BBC said Schumacher was wearing a helmet when he went down in an out-of-bounds area of the resort, but the helmet cracked on impact with a rock.
Schumacher won seven Formula One championships in his 19-year career. He retired in 2012.