A decision by GM on whether to sell a controlling stake in Opel and Vauxhall to parts maker Magna International or investment company RHJ International is still some way off, Opel Task Force member Thomas Schaefer told Reuters.

Earlier this week, GM Europe's chief negotiator John Smith said he expected a deal by the end of September. Reports suggested that a deal with RHJ could be concluded without delay but Magna's bid still needed clarification, mostly over the sale of Chevrolet-branded vehicles in Russia.

Schaefer, who is also state secretary in the finance ministry of Hesse, represents the interests of his state and three others that are home to Opel manufacturing plants. Those states and the German national government in Berlin have said that they would be more willing to grant billions of euros in state aid if GM picks Magna.

Schaefer said as long as GM is in need of aid from Germany,  a deal with Magna would be the best option.

"I believe there are only a limited number of issues still open. If one were to sit down and concentrate on working them out, a solution could be found in 24 hours," Schaefer said.