"We cannot make investment decisions without knowing what will happen," Lohscheller said.
"Brexit could disrupt supply chains in Europe as well as Britain. There are jobs and investments at stake. Everybody needs to be aware of the responsibility," Lohscheller said, adding that he wants Opel and Vauxhall to reach parent company Peugeot's level of profitability in the medium term.
Opel is getting close to reaching a 6% profit margin this year, a spokesman said.
(Reporting by Edward Taylor; Editing by Tassilo Hummel)