Delfin, the holding company of late Italian billionaire Leonardo Del Vecchio, proposed five directors which Mediobanca shareholders will be called to vote upon on Oct. 28.

The board in turn has proposed 15 members for the full board, including new terms for current Chief Executive Alberto Nagel and Chairman Renato Pagliaro.

While never questioning Nagel's reappointment, Delfin had asked instead for a change of chairman to mark a break with the past.

While Delfin's slate does not pose a direct challenge to either Nagel or Pagliaro, its move to put forward its own nominees increases uncertainty in the short term and could lead to a fractured board, analysts have said.

"The list is proposed with the aim of collaborating with all members of the board and offering a contribution to the implementation of the industrial plan," Delfin said.

It added its list had "no competitive intentions" in relation to the board's one but aimed "to bring the value of constructive change".

Delfin, now owned by Del Vecchio's heirs and managed by his former right-hand man Francesco Milleri, owns 19.8% of Mediobanca. It currently has no direct board representation.

Del Vecchio, who died last year at the age of 87, had criticised CEO Nagel for failing to grow the investment bank's business adequately and holding back expansion at insurer Generali, in which Mediobanca is the main shareholder.

If Delfin wins the most votes at the AGM, it will appoint a third of directors, getting all its five nominees on to the 15-strong board. It will only get two seats if it is the second most voted list after the board's one.

A third list is expected to be filed by fund managers' association Assogestioni.

Delfin can count on the support of shareholder Francesco Gaetano Caltagirone, who holds 9.8% of Mediobanca.

The board has instead the support of a group of Italian investors, representing a combined 10.9% stake.

Historically, Nagel has also enjoyed the support of institutional investors, who own more than 40% of Mediobanca.

(Reporting by Gianluca Semeraro and Claudia Cristoferi, editing by Valentina Za/Keith Weir)