Vladimir Petkovic is set to take legal action against Lazio over his sacking on Saturday, according to his lawyer.
The Bosnian announced in December that he would leave the capital club upon the expiry of his contract to take charge of Switzerland's national team.
However, Lazio argued the 50-year-old's negotiations with the Swiss football federation violated his contract and, after much speculation, he was replaced at the Biancocelesti helm by Edy Reja this weekend.
Petkovic's legal representative, Paco D'Onofrio, believes the club's reasoning was "unjust" and plans to take the case to the courts.
"We received notice of the sacking for just cause," he told Sky Sport Italia. "We’ll challenge the decision in the relevant legal arenas, because we consider it profoundly unjust.
"The statement released by Lazio is unique, as it doesn’t actually indicate the rule he is supposed to have broken during negotiations with the Swiss football federation.
"President of the Italian Football Coach Association, Renzo Ulivieri, also stated this week that Petkovic did not violate any regulation.
"No rule forbids a coach from reaching an agreement with others when his contract is due to expire. Besides, Petkovic signed for a national team and not a club rival of Lazio."
Meanwhile, Reja is set to return to action in the Lazio hotseat at home to Inter on Monday.