Michael Schumacher's condition has improved slightly after an operation to relieve pressure on his brain, his doctors have said.Seven-times Formula 1 world champion Michael Schumacher was fighting for his life on December 29 after suffering severe head injuries in a skiing accident in the French Alps resort of Meribel.The retired F1 driver slammed his head on a rock while skiing off-piste on Sunday morning in the French Alpine resort where he has a vacation home.'PRESSURE ON THE BRAIN REDUCED'Jean-Francois Payen, head anaesthetician at the CHU hospital in the eastern French city of Grenoble, said at a news conference: "The inter-cranial pressure was reduced. A scan showed that we have no sign that there was worsening of the initial legion."A controlled scan carried out December 31 showed that pressure on the brain was reduced."Payen added that although Schumacher's condition was "slightly better" he remains in a critical condition.Payen said: "The situation is more under control than December 30. The coming hours are critical to our strategy. Overall his condition is slightly better though we cannot say that he is out of danger.""He still remains in a coma, at the moment we still have problems with other treatments. We have won some time but we must continue an hour-by-hour surveillance"The family took the "difficult decision" to give consent for the operation, and doctors operated on Schumacher for about two hours.The medical team said: "(His) family is very much aware that his state is still sensitive and anything can happen."'BUILD-UP OF BLOOD'Head of the hospital's neurosurgery service, Emmanuel Gay, said an operation involved removing a large hematoma, the medical term for a build-up of blood, from the left-hand side of Schumacher's brain.Gay said: "It was larger and more accessible (than others). We judged we could remove it without taking any risks." He said the operation was designed to reduce, within Schumacher's skull, the pressure on the brain, which suffered injuries including lesions and contusions from Sunday's fall.INQUIRY LAUNCHEDPhilippe Quincy, the Albertville public prosecutor, told Reuters an inquiry had been launched on Sunday to identify the causes of the accident. Initial findings indicated the blow was so hard that Schumacher's helmet had shattered.Quincy said: "We know that the accident took place in an off-piste zone where rocks were partly or totally hidden by snow. Schumacher had likely been thrown off balance by one of them."CONDITIONED DETERIORATEDSchumacher was initially conscious as he was transported to a local hospital in Moutiers and then to Grenoble. However, his condition deteriorated sharply afterwards.Neurosurgeon Stephan Chabardes said an emergency brain scan carried out on Schumacher had revealed internal bleeding and injuries including contusions and lesions. He said they had operated to treat the internal bleeding.Schumacher was placed in an artificial coma but, contrary to an earlier French media report, said they had not carried out a second operation during the night and were not planning any further interventions at this stage.