FRANKFURT (Reuters) - Three more bidders are interested in taking a stake in German sports car maker Porsche, rivaling investment plans by Qatar, German magazine Focus reported on Saturday.

In an advance release of remarks due to be published on Monday, Focus said without citing sources that a Chinese and a Russian sovereign wealth fund as well as a hedge fund were interested.

A Porsche spokesman declined to comment on the report.

Porsche, which owns 51 percent in Volkswagen, is seeking an outside investor after amassing 9 billion euros (S$18.39 billion) in debt during a bungled attempt to dominate VW.

Earlier this week, Porsche said that Qatar had made an offer to the controlling Porsche and Piech families that could help reduce the mountain of debt at their wholly owned automotive holding Porsche SE. Sources told Reuters on Friday the owners were set to discuss an investment by Qatar in the next two weeks and a decision may come even before Volkswagen's supervisory board meeting on July 15.

A successful investment from Qatar could strengthen Porsche Chief Executive Wendelin Wiedeking's negotiating hand as he tries to strike a deal with VW.

Without it Porsche will struggle to prop up its finances and may have little choice but to yield to a reverse takeover from VW, Europe's biggest carmaker.

German magazine Spiegel reported Porsche CEO Wiedeking had warned the owner families of selling Porsche AG to VW.

Porsche had earlier dismissed as unworkable any deal which involved a partial sale of its sports car business to VW, noting that it would let banks call immediately a 10.75 billion euro syndicated loan they awarded Porsche in March.

(Reporting by Eva Kuehnen and Hendrik Sackmann in Stuttgart)