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Citing an internal forecast, Capital wrote in an article appearing on Thursday that Opel expects to sell 1.4 million vehicles in 2012, about 100,000 less than originally planned.
The magazine added that parent GM therefore requires Opel's management to draft by the end of January a business plan for the coming years that would ensure the business returns to profitability.
A spokesman for Opel declined to comment on the report.
Under a restructuring plan presented in February last year, Opel has targeted achieving profitability by 2012 following a 20 percent capacity reduction across Europe.
Last week, Chief Executive Karl-Friedrich Stracke said he wanted his company to reach annual profits of 1 billion euros starting in 2016 and a margin of 5 percent based on a market share of 8.5 percent in Europe.
(Reporting by Christiaan Hetzner and Christoph Steitz; Editing by David Holmes)