Three groups have entered bids for Saab, General Motor's Swedish car unit, and a preferred bidder is to be chosen by the end of this week, the Financial Times newspaper reported on Tuesday, citing sources.

The FT said Swedish luxury sportscar maker Koenigsegg and Ira Rennert's Renco Group were among the suitors, as well as Merbanco, a group of investors from the U.S. state of Wyoming.

GM is to finance the spin-off by $500 million in assets and cash, plus production equipment for a new Saab model as well as $150 million of cash already in Saab's account.

Under the deal, the new owner is to pay GM back if it succeeds in turning Saab around, the report said.

Cash amounts pledged by the three bidders vary, but it is smaller than the amount GM is contributing, the paper said.

The Swedish carmaker, which first sought protection from creditors in February, was granted an extension of its business reorganization until August 20 to line up a new owner and restructure. Saab has said it was hopeful a final deal could be agreed before mid-June.

(Editing by Dan Lalor)