Milan, April 9 - Italian merchant bank Mediobanca's board of directors on Tuesday voted to participate in a 400 million euro capital increase for struggling media firm RCS, publisher of Italian daily Il Corriere della Sera, sources close to Mediobanca's board said. Earlier Tuesday, Fiat Chairman John Elkann said his company would also participate - on a pro-rata basis - in the RCS capital increase. Mediobanca has a 13.7% stake in the shareholder pact which controls 58% of RCS and directly owns some 50 million euros in RCS debt. The stake makes Mediobanca the firm's largest single shareholder. According to the sources, the board members agreed to participate in the increase on the basis of a restructuring package which calls for the entrance in RCS's capital of an industrial partner. No potential partners have as yet emerged and no name were discussed, the sources said, pointing out that the first priority is to secure the company's financial situation. However, Mediobanca's board has not yet decided on a position with respect to eventually purchasing unsold shares, according to the sources.