Guttenberg flew to New York Sunday for talks with bankers before he will head to Washington to meet with US Treasury Secretary Timothy Geither and GM Chief Executive Rick Wagoner on Tuesday.
“It will be difficult to secure a sustainable future” for Opel without an outside investor, Guttenberg said late on Sunday.
The German government is attempting to save the carmaker – a subsidiary of beleaguered US giant General Motors (GM) – but has resisted calls to offer billions in state aid. Opel employs some 26,000 people in Germany.
Berlin is wrestling with GM's request for €3.3 billion in government funds from Germany and other European countries where it has factories. Opel has presented a "restructuring plan" which received a cool reception from the German authorities.