A report by European soccer's governing body UEFA said the continent's top-flight clubs are expected to suffer losses of more than 8 billion euros ($9.78 billion) due to the impact of the COVID-19 pandemic.
The report showed 4 billion euros were lost in gate receipts, 2.7 billion euros in sponsorship and 1.4 billion euros in broadcast revenue.
The losses led to a dip in the clubs' expenditure on transfer deals, with spending in the January window down 56% compared to last year. The 2020 summer transfer window saw a 39% decrease from 2019.
English clubs made up 43% of global transfers, with the Premier League being the biggest spender in the 2020-21 campaign at more than 1.8 billion euros.
UEFA said reforms to its financial fair play rules were necessary and that transfer fees and wages "must be reduced to acceptable levels".
The report also criticised the breakaway European Super League, saying a closed competition would have "devastating impacts on European football from a sporting, emotional and financial perspective".
The breakaway league set up by 12 clubs was announced last month but fell apart after 48 hours following a huge backlash from fans, governing bodies and politicians.
The Super League had argued it would increase revenue for the top clubs in Europe and allow them to distribute more money to the rest of the game.
"A breakaway league cannot be the response to the pandemic, the report added.
"Restoring financial health and growth requires a process of financial discipline, careful management and long-term planning.
"It is only by respecting the pyramid and the principle of promotion and relegation on sporting merit that European football will be able to continue to grow."
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