General Motors Corp. (GMGMQ) could "theoretically" sign a deal with a different bidder for the carmaker's German unit Adam Opel GmbH, government spokesman Thomas Steg said Friday.

But he said: "Negotiations with Magna are at a very advanced stage."

GM is in talks with Austrian-Canadian car parts maker Magna International Inc. (MGA) about an investment in Opel.

The German government said May 30 it selected Magna as a partner for Opel and agreed on providing EUR1.5 billion in bridge financing from the federal and state governments, paving the way for a takeover by Magna and its two Russian partners.

Fiat SpA (F.MI) has also presented a plan to acquire Opel, as has the U.S.-based investment group Ripplewood.

A Chinese bidder, Beijing Automotive Holding, has now also presented a plan for Opel. A delegation from the company has told the German government it is interested in a second chance should the deal with Magna fail.

Steg also said the government and taxpayers won't take on the billions of euros in pension burden for Opel workers, and Magna and GM are still negotiating this issue. He also said the issue of patent fees hasn't been included in Magna and GM's signed memorandum of understanding.

Handelsblatt reports Friday that GM will be getting around EUR6.5 billion for patents from Opel over the next 10 years, and that the responsibility for Opel's estimated EUR4.5 billion pension burden is an open question.

-By Andrea Thomas, Dow Jones Newswires; +49-(0)30-2888-4126; andrea.thomas@dowjones.com