Cristiano Ronaldo of Real Madrid (R) duels for the ball with Dani Alves of FC Barcelona during the Copa del Rey quarter final second leg match between FC Barcelona and Real Madrid at Camp Nou on January 25, 2012 in Barcelona, Spain.
Real Madrid and Barcelona are football's biggest moneymakers for the third straight year and look set to out-earn their rivals for the foreseeable future.
The annual review of football finance by Deloitte shows Madrid topping the list for the seventh straight year with revenue of 479.5 million (US$636.5 million) to the year ending June 30, an increase of 9 percent on the previous 12 months.
English champion Manchester United was again in third place with €367 million, the highest of four English clubs in the top 10 earners. Bayern Munich was fourth with €321.4 million, with Arsenal, Chelsea, AC Milan, Inter Milan, Liverpool and Schalke next.
One more year at the top for Madrid would equal United's No. 1 streak from 1997-2004 but the accountancy firm says on-field success could yet push Barcelona into first place next year.
Barcelona trails Madrid by seven points in the Spanish league but its revenue increased 13 percent to €451 million and it could rise further if the team retains the Champions League title.
Defending Spanish and European champion Barcelona receives about €30 million per season in a sponsorship deal from the Qatar Foundation and earned €51 million from the Champions League, beating United 3-1 in last season's final at Wembley Stadium.
It can already count on €3.5 million toward next year's total after winning FIFA's Club World Cup in December.
"This may allow it to narrow, or even bridge, the gap to Real," Deloitte sports business group partner Dan Jones said. "However, relative on-pitch performance, particularly in the Champions League, may determine next year's top two Money League placings.
"Both clubs are closing in on revenues of €500 million and are likely to pass this threshold within the next few years. Each club's annual revenues have grown by almost €200 million compared with five years before, a remarkable achievement."
United is certain to trail again next season after its early elimination from this season's Champions League, only the second time it has failed to progress from the group stage in 16 seasons.
Madrid and Barcelona have both advanced to the last 16 and have such earning power that even a move to collective bargaining for broadcast revenue - the model long employed by England's Premier League - is unlikely to affect their financial dominance.
"The gulf may widen to over €100 million next year," Jones said. "Spanish clubs are currently negotiating a collective model for the distribution of La Liga broadcast revenues, potentially from 2015-16.
"The revenue advantage that Real and Barca enjoy over their European peers indicates that a more even distribution of La Liga broadcast revenues would not necessarily challenge the two clubs' dominance at the top of the Money League."
Madrid earned 36 percent of its revenue from commercial activities such as merchandising and sponsorship, 26 percent from matchday income, including ticket sales, and 38 percent from broadcast agreements.
The top 20 clubs in the Deloitte list generated a combined €4.4 billion over the 2010-11 season, about 3 percent up on the previous year's €4.3 billion.
Tottenham rose above Manchester City to 11th place following its run to the quarterfinals in its debut Champions League campaign, but City could leapfrog its English rival next year after six matches in this season's group stage.
Borussia Dortmund, Valencia and Napoli were newcomers in the top 20, replacing Atletico Madrid, Stuttgart and Aston Villa after a season of greater domestic success.
French champion Lille was the only winner of one of Europe's five major leagues - Spain, England, Italy, Germany and France - not to make it into a top 20 entirely composed of European sides.
Deloitte said that Brazilian clubs Corinthians and Sao Paulo, with reported revenues of between €70 million and €80 million, would only make a top 50 list.