A senior member of Chancellor Angela Merkel's Christian Democrats (CDU) broke ranks with the government over the future of Opel on Thursday, saying Canadian automotive firm Magna is not necessarily the best bidder for the carmaker.

It's of secondary importance who the owner is, Guenther Oettinger, CDU premier of the southern state of Baden-Wuerttemberg, told the Rheinische Post daily.

I think Magna can do it, but I don't rule out others being able to do it as well, said Oettinger, whose state is home to roughly one in eight of Germany's population. Daimler and Porsche are based in his state but there are no Opel plants.

Merkel's government has repeatedly stressed its preference for Magna, and has offered to stump up billions of euros in aid if Opel's parent, General Motors', gives Magna the nod, passing over a rival bid from Belgian-based RHJ International.

However, doubts about Magna's offer have grown since GM declined to pick a winning bidder for Opel last weekend.

GM's management increasingly began to question the move when the U.S. carmaker emerged from fast-track bankruptcy proceedings just five days before the July 15 target. Sources close to the talks have said GM may be willing to hold on to Opel.

Berlin and the federal states that host Opel plants have already provided a loan to the carmaker worth 1.5 billion euros. German Economy Minister Karl-Theodor zu Guttenberg said on Thursday the money should last until around January.

(Writing by Dave Graham; editing by John Stonestreet)

General motors Germany