Michael Schumacher showed a slight improvement in his condition and underwent a second procedure to remove a hematoma from his brain Monday evening but doctors in Grenoble, France, continue to say the former Formula One driver faces an uncertain prognosis.

Schumacher has been hospitalized in critical condition since Sunday, when he fell and struck his head against a rock while skiing in the French Alps. The auto-racing legend, who turns 45 on Friday, has been in a medically induced coma since undergoing surgery to relieve intercranial pressure shortly after the fall. A brain scan Monday showed that pressure had unexpectedly eased in his brain and doctors at Grenoble University Hospital decided to remove one of the larger and more accessible hematomas on the left side of his brain.

“We cannot say it’s over. We can say there are highs and lows,” Emmanuel Gay, the hospital’s chief of neurology told reporters Tuesday, ” … but it’s a bit better than it was [Monday].”

Gay indicated that a number of hematomas (bruises or blood pools) on Schumacher’s brain remain and are being monitored. “Compared to yesterday, the situation has improved, but it remains fragile and critical,”  Jean-Francois Payen, an anesthesiologist and head of the intensive care unit, added (via the Guardian), “We cannot say that he is out of danger. The surgery bought us more time. The situation can improve as well as worsen.”

A general view of the “Biche” and “Chamois” ski runs at Saulire mountain near Meribel in the French Alps. This believed to be the area in which Schumacher fell. (David Ebener / EPA)

Doctors said they have not determined how long to maintain Schumacher’s coma, which is medical protocol for preventing further brain damage in cases of severe trauma.

“We cannot tell you any more about the future,” Gerard Saillant, a family friend who is in Grenoble and is a surgeon, told the Associated Press.

Schumacher, the most successful driver in Formula One history with seven world titles and 91 victories, was skiing with his 14-year-old son, Mick, when he fell during an off-piste (off course) run at Meribel. He was wearing a helmet, which doctors credited with saving his life. His manager, Sabine Kehm, said that the helmet had cracked on impact.  “It looks like probably that initiating a corner, he was hitting a stone which he had not seen and was catapulted down on a rock,” Kehm said (via the AP). “That is extremely and very unfortunate … really very, very bad luck. Michael was not at high speed.”