The 27-year-old Argentinian has been frozen out of the first team since revealing his intention to leave the club in the summer.
Vincenzo D'Ippolito, Ledesma's agent, told ANSA: "Ledesma was willing to be reintegrated into the squad even without signing a contract extension. But when the President demanded an apology, the lad, not seeing any reason to give one, decided to start an appeal.
"He did it for a question of personal and professional dignity. He really hoped for a reintegration. Last June, he accepted an extension proposed by the club. The only condition that he put forward was that of being free to leave in case of an important offer from a big club.
"Then this possibility vanished because Juventus contracted Felipe Melo and Milan didn't want to sell Pirlo anymore. But the lad was willing at that point to stay at Lazio and had refused proposals from Fiorentina, Genoa and Udinese. Only then this contract disappeared."