At the helm of the Italian bank since 2008, Nagel has come under fire in the last two years from two major shareholders - the Del Vecchio family's holding company Delfin and Italian tycoon Francesco Gaetano Caltagirone - who hold 19.8% and 9.8% stakes, respectively, in the bank.

Both blamed him for not adequately growing the investment bank's business and for hampering the expansion of insurer Generali, in which Mediobanca is the main shareholder.

The bank's board is elected for a three-year term and the current term expires on Oct. 28 when Mediobanca shareholders will vote on renewing the board, including the CEO.

Last week, Mediobanca's board filed its own slate of nominees, advocating that Chairman Renato Pagliaro and CEO Nagel remain in place for another three years.

The group of investors, who in 2018 signed a consultation agreement on the most important issues regarding the bank, met on Monday.

After the meeting, the president of the group of investors, Angelo Caso, said in a statement that "the consultation pact strongly supports the bank's management and hopes that the next board of directors will be able to continue the work" set out in the plan through 2026 unveiled by Nagel at the end of May.

Another member of the group, who did not wish to be identified, said all members of the group would vote to keep Nagel as CEO.

"The members of the agreement will vote as always for the outgoing board list," the group member said after the meeting of the shareholders' group, which includes Banca Mediolanum and some Italian entrepreneurs among other shareholders.

Delfin, which previously tried but failed to agree a common list of board nominees with the existing board, is set to file a separate list of nominees for the new board, two people close to the matter said, but it is not expected to put up a direct challenger to either Nagel or Pagliaro.

Nagel has so far enjoyed the support of institutional investors who collectively account for 45% of the bank's capital.

(Reporting by Gianluca Semeraro, editing by Susan Fenton)