Roy replaced as Nice coach
"Eric has not failed. We need a sporting manager, someone who knows the club well," club president Jean-Pierre Riviere told newspaper Nice Matin.
Nice have got off to a disappointing start to the Ligue 1 season and lie 17th with 11 points from 13 games.
"Rene Marsiglia knows the game and the players. He is up to this challenge," Riviere said.