European football clubs could lose an estimated 5.2-6.3 billion euros (6.08-7.37 billion U.S. dollars) in revenues due to the impact of the COVID-19 pandemic, European Club Association chairman Andrea Agnelli said on Thursday.

Finances at football clubs across the region have been stretched as the health emergency forced authorities to suspend matches or limit spectator numbers once championships had restarted.

"Without competitions, we don't have access to certain items in our economic accounts and without these the system becomes unsustainable," Agnelli, who also serves as the Juventus chairman, told a shareholder meeting of the Italian Serie A club.

"We will only be able to assess the impact of this situation in its entirety in the autumn of 2021," he added.

Agnelli said the forecast included stadium losses, the impact the emergency had on medium-to-long-term commercial agreements and TV rights contracts that had to be renegotiated.