Lyon president Jean-Michel Aulas has warned of "a real problem" looming for many French clubs if the decision to cancel the 2019-20 season is not overturned.
Aulas has been vocal in his opposition to voiding the remainder of the Ligue 1 campaign, which left Lyon in seventh place in the table and without a spot in next season's Champions League.
Having seen the Bundesliga resume the 2019-20 season and with the Premier League, LaLiga, and Serie A potentially following suit, Aulas said French football could find itself being left behind.
Defending his decision to appeal against the cancellation of the season by writing to the French prime minister and sports minister, Aulas told Franceinfo: "We see an abnormal difference in competitiveness between European countries.
"[There will be] between 800 and 900 million euro losses as of June 30 for French football.
"As we were unable to show our good faith as we would have wanted, or show that it made economic sense and the best thing for Europe to finish all our games, so unfortunately we've had to seek an alternative in the interest of those immediately concerned and in the general interest."
Lyon finished third in 2018-19 and were still in the Champions League and the Coupe de la Ligue when football in France was postponed due to the coronavirus pandemic.
Aulas indicated the financial impact of the season's termination would not cause Lyon serious problems, but he said French clubs would lose out in the transfer market.
"Obviously, transfers will be put on hold. It's looking like we will have to stop the championship so players will not be seen," he said.
"Clubs which can eventually invest, well clubs abroad have had their season put back and they will finish it later. This is all going to cause a real problem for French clubs – a loss of several hundred million euros.
"Transfers agreed a few years ago also may not be honoured, so it's going to cause problems. Many French clubs will be in financial difficulties."