Doctors said a brain scan had shown "areas of cerebral contusions", but the extent of the injuries was unclear and more tests were being conducted. "He is still in intensive care and his condition remains very serious," a statement from the hospital said.
Mr Lopez, 56, will remain under observation until doctors decide whether surgery will be necessary. He took a severe blow to the head when his Audi 80 smashed into a truck.
Mr Lopez became famous for introducing revolutionary measures to cut costs in the car industry in the early 1990s. He defected from General Motors to Volkswagen early in 1993, and implemented hardline measures which helped put the ailing German car-maker back into profit.
However, his reputation was tainted by allegations by General Motors that he stole confidential documents and gave them to Volkswagen. He denied this but was forced to resign in 1996.