Andrea Della Valle has stepped down as President of Fiorentina with immediate effect, leaving the future ownership of the Serie A club unclear.
His older brother Diego Della Valle owns Fiorentina, having re-formed the Florence club in 2002 after a bankruptcy under the ownership of Vittorio Cecchi Gori.
"During today's board meeting, Andrea Della Valle has announced his decision to leave the presidency of the club," read an official statement from Fiorentina, which did not specify what the decision meant for Diego.
It did, however, confirm that vice-President Mario Cognini will temporarily move up to take charge.
No reason was given for the widely expected announcement, with media speculation blaming his wish to spend more time in the family's luxury goods business Tod's.
Other reports said he was unhappy with the reaction of some Viola supporters, who were upset by the sale of Brazil midfielder Felipe Melo to arch-rivals Juventus this summer and for the club's lacklustre transfer activity.
The Della Valle brothers have dragged Fiorentina back up the Italian league after they were forced to reform in the fourth tier in 2002 following financial problems.
Just two years later the club returned to Serie A and although involved in the Calciopoli scandal in 2006, they have thrived and are again competing in the UEFA Champions League this season.
Despite the upheaval, the statement added that the board were still committed to a new stadium following talks with Florence city officials this week.
The "Cittadella Viola" plan envisages not just a new stadium but an area of the city devoted to the club.
Fiorentina, who like most Italian clubs are forced to rent the Stadio Artemio Franchi from the local council, made clear that they were prepared to contribute funds for the new stadium.
"The Cittadella Viola is not a gift to the city of Florence but to Fiorentina, but we believe that it is a great opportunity for the city of Florence: the millions of more tourists that will be attracted here and the many jobs it will create. Large investments will be required but there is no cost to the taxpayer."
By not owning their own stadiums, clubs in Italy have lost out on revenue compared to their English and Spanish counterparts and have suffered in European club competitions as a result.
Juventus are the first Serie A club to build their own stadium, with completion due in 2011. Roma will hold a news conference on Tuesday to announce plans for a new ground, while Inter, Lazio and Sampdoria have also previously talked about building their own stadia.