Mr zu Guttenberg has he has to think of taxpayers needs
Germany's economy minister has said the government couldn't afford to spend all the money required to save every threatened job at carmaker Opel.
With Fiat continuing talks to buy Opel from General Motors, the Italian firm has already warned that one Opel plant in Germany will likely close.
Fiat wants loan guarantees from the German government to secure the deal.
Karl-Theodor zu Guttenberg said the government "had an obligation to deal responsibly with taxpayer's money".
The comments of the economy minister came in an interview with German magazine Der Spiegel.
He added that he remained open to both Fiat's bid, and the lesser interest expressed by Canadian car parts business Magna.
"Both concepts, both Magna's and Fiat's, still include open questions that need to be cleared up," said Mr zu Guttenberg.
"For the time being, I view both concepts with the same openness and scepticism."
General Motors has a deadline of 1 June to successfully restructure its loss-making group-wide business, or else it will likely need to go into US bankruptcy protection.
While this will enable it to continue trading while protected from its creditors, it may complicate any sale of Opel, and UK sister brand Vauxhall, to Fiat.
Mr zu Guttenberg said that to prevent any difficulty, he said he was proposing that ownership of Opel be temporarily handed to a trustee.
Opel employs 26,000 people in Germany, nearly half the total European workforce of the wider GM Europe group.
The factory at risk of closure if Fiat's bid is successful, is the Opel engine plant at Kaiserslautern in Rhineland-Palatinate.
It is vulnerable because Fiat already makes the same engines at one of its factories in southern Italy.
The state premier of Rhineland-Palatinate said on Friday that his fears for the future of the factory were now "very, very big".
His comments came after a meeting with Fiat chief executive Sergio Machionne.