Leonardo told a Paris court his 14-month ban for barging into a referee prevented him from becoming Paris Saint-Germain coach as he continues his battle to overturn the hefty suspension.
• Johnson: Blanc tactics seal win
Leonardo, 44, was banned from carrying out all official matchday duties after being found to have deliberately collided with referee Alexandre Castro following Paris Saint-Germain's 1-1 draw at home to Valenciennes on May 5.
Prior to his suspension, which prevents him from going to the dressing room or dug-out on matchdays, he had been tipped to move from his role as sporting director at the Parc des Princes to succeed Carlo Ancelotti as first-team coach.
Instead, Leonardo was forced to work feverishly to find a replacement for the Italian following his departure for Real Madrid, eventually settling upon Laurent Blanc just days before the start of preseason training after reportedly being rejected by a number of high-profile tacticians.
"It stops me from working completely," Leonardo, who is seeking to prevent the FFF extending his ban worldwide, told Paris' Administrative Court on Tuesday. "I was supposed to become PSG coach, but the ban stops me sitting on the bench.
"I can't go to a club and tell them I can't do this or that. I can't even play in an amateur league anywhere in the world. It stops me sleeping."
Leonardo, who stepped down as PSG's sporting director after completing the transfer of Edinson Cavani in July, had hoped France's Olympic Committee (CNOSF) would rule on the matter, but last month the body declared itself unable to make a judgement, forcing the former AC Milan and Inter Milan coach to take his case to the court.
"What motivates me is the actual ban, not only the way it was handed down," claimed the 1994 World Cup winner, who argued the FFF could not ban him because he was not under licence with them during his two-year stay in the French capital. "But because the CNOSF declared itself unable to judge me, I am obliged to focus on the procedure."
The former PSG player, who was initially banned for nine months by the French Football League (LFP) before it was extended upon appeal by the FFF, played the court television pictures of the incident with Castro, hoping to prove he did not intend to clash with the official.
The FFF countered Leonardo's argument by saying his role as PSG's sporting director was sufficient to give them the right to sanction him.
The court is expected to hand down its verdict on Friday at the earliest, though a decision is more likely to be made public on Monday.
Should the court rule against Leonardo, he could still take his case to the Court of Arbitration for Sport.