Koenigsegg has withdrawn its offer to buy Saab, GM has confirmed.
Details are scarce, but GM President and CEO, Fritz Henderson said: "We're obviously very disappointed with the decision to pull out of the Saab purchase.
"Many have worked tirelessly over the past several months to create a sustainable plan for the future of Saab by selling the brand and its manufacturing interests to Koenigsegg Group AB.
"Given the sudden change in direction, we will take the next several days to assess the situation and will advise on the next steps next week."
Koenigsegg announced its decision in a statement.
"We regret that after six months of intense and goal-oriented work we have come to the painful and difficult conclusion that we are not going to be able to carry out the acquisition of Saab Automobile," the head of the company, Christian von Koenigsegg, said.
"The time factor has from the beginning been critical for our strategy to breathe new life into the company. Unfortunately, delays in completing the deal have led to risks and uncertainties that prevent us from successfully carrying out our business plan for Saab Automobile."
GM and Koenigsegg had announced a preliminary agreement over the sale of loss-making Saab in June, and spent the following months working on confirming the deal.