A study by auditing firm KPMG showed that Bayern Munich were the only title winners in Europe's eight major football leagues to make a profit in the coronavirus-hit 2020-21 season.
The Bundesliga champions scrapped into the black with a tax benefit of 1.8 million euros ($A2.8 million), as well as the lowest ratio of cost to staff, recording operating revenue at 58 percent.
Andrea Sartori, sports chief at KPMG, said: "The reopening of the stadia and some of the major commercial deals recently signed may provide some optimism ... the pandemic only exacerbated the financial stability issues and the fragility of the football ecosystem."
To exemplify those problems, Serie A winners Inter Milan posted an annual loss of 245.6 million euros ($A382m) on operating revenue of 347.5 million ($A541m).
In addition, La Liga champions Atletico Madrid lost 111.7 million euros ($A174m) on revenue of 349.6 million ($A544m).
Top of the revenue table was Premier League champions Manchester City, which generated 644.2 million euros ($A1.02 billion), up 17 percent from the previous season, the study showed.
City, who reached the Champions League final for the first time, beat local rivals Manchester United in revenue of 557 million euros ($A878m).
Bayern were second only to City with revenues of 597.5 million euros ($A942m), while Turkish Super Liga winners Beikta had the lowest revenue among the eight champion clubs with 59 million euros ($93m).
Six clubs increased broadcast revenue, benefiting from deferred income related to matches postponed from the 2019-20 season and matches played after June 2020.