RAG, a public sector foundation and the controlling shareholder of German chemicals group Evonik, was not immediately available for comment.
Thyssenkrupp, whose supervisory board was meeting on Wednesday to review offers for its elevator division, declined to comment.
A local player with less strict return targets than private equity, RAG's involvement may improve the consortium's chances with labour representatives, who control half of Thyssenkrupp's supervisory board and need to approve any deal.
On Monday, RAG sold a 5.2% stake in Evonik worth 632.5 million euros ($705.9 million).
(Reporting by Arno Schuetze, Tom Kaeckenhoff and Christoph Steitz; Editing by Michelle Martin and Susan Fenton)