German Economy Minister Karl-Theodor zu Guttenberg has said it is "hardly realistic" for GM to hold on to Vauxhall and Opel rather than sell them.
Speculation has suggested that GM's failure to decide between potential buyers Magna and RHJ would lead to it holding on to Vauxhall and Opel itself.
But Guttenberg told the German newspaper Frankfurter Allgemeine Zeitung that GM had put forward the possibility of keeping Opel last March.
He said that the high costs of restructuring Opel and Vauxhall - estimated at around £2.5 billion - mean that GM cannot afford to keep the unit.
At present, Vauxhall and Opel are surviving on a six-month 1.5bn euro (£1.3bn) bridging loan from the German government that matures at the end of November, when a new investor had been expected to take control.
However, Guttenberg has now said that the money provided should last until around January.