Nick Reilly, head of international operations for General Motors Co. and interim chief of the auto maker’s European Adam Opel GmbH unit, says today the auto maker’s German unit and its U.K. sister Vauxhall must slash capacity 20% to 25%.

It is widely expected the capacity cuts will come at the cost of at least one Opel facility and affect some 10,000 jobs. Opel employs 50,000 people across Europe and half of those are in Germany.

“We are still finalizing details of the plan,” Reilly says in new blog he started to keep journalists and other interested parties up to speed on GM’s turnaround plan for Opel.

Blogging from Spain on the final stop of visits to Opel/Vauxhall facilities, labor unions and government officials, Reilly says he will meet with European Union officials regarding GM’s intentions for the brands next week.

GM backed out of a deal to sell a majority stake of Opel to Canadian parts maker Magna International Inc. two weeks ago, saying its financial fortunes in the U.S. had improved so it would restructure the unit on its own.

The decision riled Opel labor unions and the German government, which negotiated the sale for eight months.

GM installed Reilly, a veteran of Vauxhall, to begin the turnaround while the auto maker searches for a permanent CEO for Opel.

Reilly says he expects to have a new plan, estimated to cost €3.3 billion ($4.9 billion) and hinging on government support, presented to interested parties by mid-December.

“Time is not on our side,” he writes. “I cannot make excuses for things done in the past, but we can move forward.”