Sedran, 47, joined Opel in April as a top executive in charge of strategy. He has played a role in Opel's efforts to stem years of losses, both as an outside consultant at turnaround firm AlixPartners and at Opel.
The Opel board of directors on Tuesday named Sedran deputy chairman of the management board, the top management body, and said he would act as interim chairman of that group until a permanent replacement for Stracke can be found. Management board chairman is the German equivalent of CEO.
The company said Sedran would keep his current job as chief of operations, business development and corporate strategies.
"We will continue to implement our business plan as it was outlined and work to improve it. We will further reduce bureaucracy and continue to challenge the corporate culture," said Opel board of directors chairman Steve Girsky, who is also vice-chairman of the GM board.
While Stracke served as both head of Opel and as president of GM Europe, Sedran takes over only the interim Opel post.
The title of president of GM Europe remains with Girsky, who assumed control of the company's European operations after Stracke left.
Stracke, who served as both CEO and head of GM Europe, resigned just two weeks after presenting a plan to improve the struggling Opel and Vauxhall brands in Europe. The plan included new models in areas where the company was not represented and cost savings through an alliance with France's PSA Peugeot Citroen. The company was in talks with employee representatives that foresaw closing its plant in Bochum, Germany, in 2017 and asking employees to forego a recently bargained raise.
GM head Dan Akerson praised Stracke, who is to work on special projects for the company. But industry experts say Stracke's departure may be a sign that GM is impatient with the pace of restructuring its European business and ending losses there. The company faces obstacles to rapid restructuring such as labour contracts that forbid layoffs until 2015 and the German practice called "co-determination" that gives employee representatives seats on the board of directors.
Some analysts also think that Girsky may be positioning himself to bid for the top job at GM by leading a successful turnaround at Opel. Edmunds.com analyst Michelle Krebs has said that "turning around GM's operations in Europe would be a huge step toward the throne."