FRANKFURT - Opel interim CEO Stephen Girsky said changes have to be made at the carmaker to revitalize it, German daily Bild said citing his e-mail to staff.

"Our successful revitalization demands from all of us the readiness to do things differently in the business and at the same time to act quickly," Girsky said.

General Motors named Girsky to his position at Opel when it announced on Thursday that CEO Karl-Friedrich Stracke had stepped down, in a surprise move analysts said showed the U.S. carmaker's growing impatience with 12 years of losses in Europe, reported Automotive News.

IG Metall trade union head Berthold Huber warned GM against breaking an agreement with labor on guarantees for jobs and keeping manufacturing plants in Germany, according to an interview with Sueddeutsche Zeitung.

"I can only warn it. Whoever wants to give up on Opel ought to know: those could be the most expensive closures of plants which a company would ever attempt in Germany," he said.

A spokesman for Opel said late on Friday the company would not need to draw up a new mid-term business plan following a decision by GM to abruptly replace Stracke.

Two weeks ago, the supervisory board for Opel approved a mid-term business plan, which runs through 2016, in a step toward returning to profitability. But real savings in a restructuring will not come until GM negotiates a deal with labor unions to close the Bochum, Germany, plant after 2016.