Sabine Kehm told reporters that his condition has not changed since doctors said he showed small signs of improvement on Tuesday, following his second operation.
Schumacher, who turns 45 on Friday, suffered critical head injuries when he fell and struck a rock while skiing Sunday morning during a family vacation at Meribel in the French Alps. His 14-year-old son, Mick, was with him in a group of friends when the accident happened in a small, rock-strewn area of open ground between two groomed pistes.
The seven-time F1 champion has since undergone two brain operations and remains in a medically induced coma.
"The good news for today is ... there's no significant changes," Kehm told reporters gathered outside the Grenoble hospital where he is being treated.
"However, it is still very early, and the situation overall is critical. Everything can change immediately," she added.
Doctors have refused to give a prognosis for Schumacher, saying they are focused on his immediate care. They are trying to reduce swelling in his brain by keeping him in a coma and lowering his body temperature to between 34 and 35 degrees Celsius (93.2 and 95 degrees Fahrenheit).
Kehm said Schumacher was surrounded by his family - including his wife, daughter and son - and that there is always somebody with him.
"They are trying to support him by being by his side," Kehm said.
One visitor returning to the hospital Wednesday was Jean Todt, president of the FIA motor racing governing body and team principal at Ferrari when Schumacher won five straight F1 titles from 2000 to 2004.
Schumacher is the most successful F1 driver in history, racking up a record 91 race wins. He retired from Formula One in 2012 after garnering an unmatched seven world titles.
His accident has drawn immense media attention, and Kehm confirmed Wednesday that earlier in the week security at the hospital stopped a journalist who was posing as a priest from approaching Schumacher.
"Security got him before he got close," she said.
Schumi, as his fans affectionately call him, was famously aggressive on the track and no less intense off-hours. In retirement, he remained an avid skier, skydiver and horseback rider.
Kehm said the Schumacher family traditionally spends Christmas and New Year holidays at Meribel, where they own a chalet, and to celebrate the German racer's birthday.
___ DiLorenzo reported from Paris.