Sabine Kehm rejected as "speculation" new reports in the French media that the Formula 1 champion was gradually being woken from his coma, but said he remained in a "stable" condition.
Michael, 45, suffered a severe head injury on 29 December, when he fell and hit a rock while skiing in the French Alps resort of Meribel.
On Wednesday, L'Equipe reported that Michael is gradually being woken up from his medically induced coma, and has "reacted positively" to the process.
Manager Sabine did not deny the report, but urged fans to ignore anything other than official comments about his health.
"I am stressing again any statement regarding Michael's health not coming from the doctors treating him, or from his management, must be considered as speculation," she said. "I repeat, we will not comment on any speculation."
She told local newspaper, Le Dauphiné Libéré, "Michael's condition is still considered as stable.
"I also repeat that Michael's family is very happy and confident with the work of the team of doctors treating Michael and they trust them completely."
Michael's wife Corinna, 44, daughter Gina, 16, and son Mick, 14, have been by his bedside since the accident, and have received hundreds of letters and gifts from around the world.
They issued a statement thanking the public for their support.
"We are deeply touched by all the messages to get well soon for Michael which are still being sent. That gives us strength. Thank you all so much. We all know he is a fighter and will not give up."
Meanwhile, Ferrari – the racing team with which Michael had 72 of his 91 Formula One wins – said in an online statement it was "waiting" for his return.
"Dear Michael, having spent so many years at Ferrari, you became one of us. You thrilled us so often, bringing us great joy, but the greatest one is yet to come: namely seeing you here in Maranello again, to meet your second family, the Ferrari one."