Madrid topped the table for the 11th year running with earnings of €577 million over the course of the season, driven largely by a €22.7 million increase in commercial revenue.
Barcelona, buoyed by on-pitch success that included a La Liga, Spanish Cup and Champions League treble, climbed from fourth place to second place with revenues of €560.8 million, bumping United down to third.
When Messi and Barcelona conquered all
"For the first time, the top three clubs in the Football Money League have all passed the 500m euros revenue mark," said Dan Jones from Deloitte's Sport Business Group.
"FC Barcelona's on-pitch achievements in the 2014-15 season have translated to financial success. The European champions have climbed to second place at the expense of Manchester United, with revenue growth across all areas of the business -- matchday, broadcast and commercial."
Barcelona's president Josep Maria Bartomeu told the Financial Times last month that the club aim to become the first to make one billion euros in a year by 2021.
Their plans include a €600 million renovation of the 93,000-capacity Camp Nou and the opening of more overseas offices.
Madrid players prefer Zidane to Benitez, says Ronaldo
Combined revenue for the top 20 clubs in the list rose eight percent to €6.6 billion -- a new record.
German champions Bayern Munich fell to fifth, their lowest placing since 2006-07, with Qatar-backed French champions Paris Saint-Germain overtaking them following another year of growth.
Manchester City, Arsenal, Chelsea and Liverpool, from the all-powerful English Premier League, round out the top 10 along with beaten Champions League finalists Juventus.
Juventus were joined in the top 20 by Serie A counterparts Roma, who climbed from 24th to 16th, but Italian heavyweights AC Milan and Inter Milan slipped to 14th and 19th respectively.
United paid the price for failing to qualify for the Champions League in 2013-14, the first season following the retirement of legendary manager Alex Ferguson.
But the club's return to the competition under Louis van Gaal -- albeit one that concluded with a group-stage exit -- and a strong commercial operation could see them bounce back to top the list for 2015-16.
"The return to Champions League football, as well as the commencement of a number of significant commercial partnerships, will only strengthen the business in 2015-16," said Deloitte's Tim Bridge.
"With this in mind, it would not be surprising to see United top next year's Money League for the first time in 12 years, with the club forecasting revenues of around around €650 million."
In total there were nine Premier League clubs in the top 20, while 17 of the top 30 revenue-generating clubs played in the English top flight in 2014-15.
England's grip on the list is unlikely to weaken anytime soon, with new television rights deals worth an estimated €10.4 billion due to kick in later this year.
Top 20 clubs in Deloitte Football Money League 2014-15 [2013-14 position and revenue in brackets]:
1. (1) Real Madrid (ESP) 577 (549.5)
2. (4) Barcelona (ESP) 560.8 (484.8)
3. (2) Manchester United (ENG) 519.5 (518)
4. (5) Paris Saint-Germain (FRA) 480.8 (471.3)
5. (3) Bayern Munich (GER) 474 (487.5)
6. (6) Manchester City (ENG) 463.5 (416.5)
7. (8) Arsenal (ENG) 435.5 (359.3)
8. (7) Chelsea (ENG) 420 (387.9)
9. (9) Liverpool (ENG) 391.8 (305.9)
10. (10) Juventus (ITA) 323.9 (279)
11. (11) Borussia Dortmund (GER) 280.6 (261.5)
12. (13) Tottenham Hotspur (ENG) 257.5 (215.5)
13. (14) Schalke 04 (GER) 219.7 (214)
14. (12) AC Milan (ITA) 199.1 (249.7)
15. (15) Atletico Madrid 187.1 (169.9)
16. (new) AS Roma (ITA) 180.4 (127.4)
17. (19) Newcastle United (ENG) 169.3 (155.1)
18. (20) Everton 165.1 (ENG) (144.1)
19. (17) Inter Milan (ITA) 164.8 (162.8)
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