Borussia Dortmund defender Mats Hummels has denied making any promise to join Manchester United.
Real Madrid have completed the signing of Brazil international right-back Danilo from Porto on a six-year deal.
A haul of 19 points from the Corsicans' first 18 games in the top flight following promotion has not been deemed sufficient for club chairman Alain Orsoni, who revealed an atmosphere of growing unrest among the players forced his hand.
He told ac-ajaccio.com: "I met the players individually and I concluded that there is a clear break between the group and our coach. So I finally decided Alex Dupont will no longer be our coach as of today.
"The situation we have today is unacceptable. Particularly worrying is the state of mind of the group, I can not find the values that have traditionally been our strength.
"I do not feel solidarity, selfless commitment and combativeness, which are essential to maintain an elite level."
Dupont's assistants Stephane Paganelli and Thierry Debes will take control of first-team affairs while Orsoni finalises a move for a new head coach, who he promised would arrive "very soon".
The Corsicans, who boast former Chelsea striker Adrian Mutu among their key players, lost 3-2 to fellow strugglers Troyes on Saturday and sit 14th in the Ligue 1 table.