Paris Saint-Germain midfielder Blaise Matuidi is being taken to court by his former agent, who claims he was poached by a rival.
Jean-Pierre Bernes, 56, has brought a case for breach of contract against Matuidi, 26, who wrote to him to end their working partnership on March 16.
Bernes, whose agreement with the France international had been due to expire on June 30, is demanding €3.5 million in damages from Matuidi and a further €5 million from rival agent Mino Raiola, whom he believes provoked the situation.
"According to FIFA and French rules, an agent must not contact a player under contract [with another agent]. Mr Matuidi was approached by Mr Raiola. That's an established fact," L'Equipe reported Bernes' lawyer, Carlos-Alberto Brusa, as saying.
"While Mr Bernes pays his taxes in France, he is up against an Italian agent whose licence is held in the Netherlands and whose company is based in Monaco.
"The sums Mr Raiola receives in France do not produce a single cent of tax. This absurd situation has to be resolved."
Raiola, who represents Matuidi's PSG team-mates Zlatan Ibrahimovic, Maxwell and Gregory van der Wiel, potentially also faces investigation by FIFA and the French Football Federation (FFF).
Bernes is determined to level the fiscal playing field for agents, echoing the stance being taken by many Ligue 1 presidents on the tax status of newly-promoted principality club Monaco.