Bordeaux said on Sunday they had temporarily placed Sertic under protection after the 27-year-old, according to regional daily Sud Ouest, received the threatening messages at his home.

"To reassure the player, we put him under protection during (Saturday's) trip to Nancy," Bordeaux president Jean-Louis Triaud told AFP. "We also monitored his house but the protection has since been lifted."

The UNFP slammed the treatment of the player, while praising Bordeaux for acting swiftly to guarantee his safety.

"So a player was threatened with death for expressing his desire for a change of scenery, and his club, taking things very seriously and so much the better, had to work to protect him. Him and his partner!" railed the UNFP.

The union also issued its "unconditional support" for Anthony Mounier, whose move from Bologna to Saint-Etienne provoked a strong backlash from a section of supporters.

Reports in France suggest his loan deal will be cancelled, with Mounier an unpopular arrival at Saint-Etienne having come up through the academy at bitter rivals Lyon.

Mounier is also reported to have received "death threats", via both "social media and over the phone", according to Le Parisien.

"Needless to say we never imagined that one day we would be under an obligation to support footballers for their right to practise their profession in France, simply to protect their moral and physical integrity and that of their family?" the union deplored.