European football is "beginning to see the scale" of the financial impact of the coronavirus pandemic after a £3.4bn fall in revenue in 2019-20, according to finance company Deloitte.
Overall revenue fell to £22.1bn, with most European leagues halting in March 2020 before resuming without fans.
It is the first reduction since the global financial crisis of 2008-09.
Deloitte's Dan Jones said its report "only accounts for, in most cases, three months of Covid-19 impact".
He added: "It will be a number of years before the full financial impact of the Covid-19 pandemic on European football is known.
"But we're now beginning to see the scale of the financial impact that the pandemic has had on European clubs."
Deloitte's annual review of football finance shows that clubs across the English Football League's three divisions reported a combined reduction in revenue of 13% (£150m) to £943m.
Deloitte said in June that the combined revenue for Premier League clubs in 2019-20 dropped by about 13% (£648m) to £4.5bn.
When combined with Europe's other 'big five' leagues, the cumulative revenue decline was 11% (£1.8bn) to £13.2bn.
The report stated that, while EFL clubs had shown "remarkable resilience", the figures from almost a full season without matchday revenue (2020-21) would "be sobering".
However, with clubs around Europe hoping to welcome back near-capacity crowds from the beginning of the new season, there is hope the finances of clubs will improve.
"Despite the uncertainties of the past year, football - and the public interest in it - has shown great resilience," said Jones.
"We are hopeful that the 2021-22 season will be a step towards normality, resulting in a strong recovery in revenue terms across the coming seasons."