BERLIN, Sept 25 (Reuters) - Poland's Unimot has emerged as one of the possible buyers of a 37.5% stake oil major Shell owns in Germany's PCK Schwedt refinery, two people familiar with the matter said.

The refinery, which is majority-owned by Russia's Rosneft , has been a problem for the German government ever since Berlin ended its energy ties with Moscow last year.

As a result, Germany put Rosneft's 54.17% stake under trusteeship, essentially giving the government control over the asset while technically leaving ownership in the Russian group's hands.

That led Shell to revive plans to sell its stake in Germany's fourth-largest refinery, which supplies 90% of Berlin's fuel, earlier this year.

"Unimot is one of the possible buyers of the Shell share, but not the only one," a government source told Reuters.

Unimot last year said it was expanding international trading as it sought to import diesel to Germany amid European Union sanctions on Russian oil and refined products.

Germany is also no longer considering Kazakhstan's KazMunayGas and its subsidiary Kaztransoil as possible buyers of the stake as they cannot guarantee the necessary stability for Schwedt, the source added.

Shell, Unimot and Germany's Economy Ministry, which is responsible for the trusteeship of Rosneft's stake in Schwedt, all declined to comment. Rosneft Germany did not immediately reply to a request for comment. (Reporting by Riham Alkousaa and Andreas Rinke in Berlin; Additional reporting by Anna Koper in Warsaw; Editing by Christoph Steitz and Sharon Singleton)