The 21-year old Argentinean was airlifted to hospital after the accident in Buenos Aires which killed three of his friends with damage to his lungs.
River Plate club doctor Hugo Cavallieri said the next few days would be extremely important in Buonanotte's recovery.
"Diego is stable but we are continuing to wait," said Cavallieri.
"We know that the next 72 hours are those where the risk is greatest.
"The fractures can wait, the priority is the lung. At the moment he is recovering as has been foreseen. The recovery period is an estimated seven months.
"He is sedated but you can talk to him because he is conscious.
"We have not mentioned at all what happened in the accident. He hasn't asked us either. We don't want him to watch television. We will supply a group of psychologists and psychiatrists to help him."