Last season, Barcelona made more money than any other club in Europe for the first time.
The Spanish club had £ 741.1m in revenue in the 2018/19 season, according to Deloitte's Football Money League.
Real Madrid swapped places with Barca, dropping to £ 667.5m in second place, Manchester United in third place to £ 627.1m.
The Reds Devils are said to have "the risk of losing their position as the top-selling club in the Premier League for the first time next year."
Who makes up the top 20?
|Most club earnings in 2018-19|
|position||team||Revenue £ (2017-18 figure)|
|Source: Deloitte Football Money League|
|2||real Madrid||667.5 (665.2)|
|3||Manchester United||627.1 (589.8)|
|4||Bayern Munich||581.8 (557.4)|
|5||Paris St-Germain||560.5 (479.9)|
|6||Manchester City||538.2 (503.5)|
|12||Borussia Dortmund||332.4 (281)|
|11||Atletico Madrid||324 (269.6)|
|14||Inter Milan||321.3 (248.7)|
|18||West Ham||190.7 (175.3)|
Why are Barcelona top?
In the 23rd edition of Deloitte's Football Money League, the gap between the first and second editions (€ 83 million) has never been so great.
Barca's significant year-over-year increase in revenue is due to the club taking on its own merchandising and licensing activities.
Dan Jones, partner of the Sports Business Group at Deloitte, commented: "Barca is a clear example of a club that is adapting to changing market conditions, reducing dependence on broadcasting revenues and focusing on growing revenues that are under its control."
Deloitte expects Barca to remain number one next year, declaring that the Catalan club is well on the way to achieving its stated goal of being the first to generate sales of over a billion euros in the coming years generate.
What is going on in Old Trafford?
Deloitte believes there are "many ways to examine the relative wealth or value of football clubs," but the revenue metric is extracted directly from the clubs' degrees.
Radio business money is the most important for clubs, accounting for 44% of total revenue.
Manchester United's revenue rose from GBP 589.8 million to GBP 627.1 million year-on-year, but forecast revenue for the 2019-20 period is between £ 560 and £ 580 million, also because the club is not committed to the Champions League could qualify.
Deloitte said these numbers "would likely cause the Red Devils to drop to their lowest Money League position in the next issue."
"This could also put the club at risk of losing its position as the Premier League's top-selling club for the first time in Money League history," added Deloitte.
Sam Boor, senior manager at Sports Business Group at Deloitte, said: "The impact of participation and performance in UEFA club competitions on revenue is evident in London and the North West. Arsenal's relative defeat is a direct result of the fact that Team did not take part in the competition for the second season in a row. This fate could also affect Manchester United. "
Spurs rule London
With eight teams, the Premier League makes the largest contribution to the top 20 in the Money League.
Tottenham reached the highest position ever with sales up 21% to £ 459.3m.
Deloitte said the jump was due to higher revenue from commercial sources and broadcasters after Spurs reached the Champions League final and moved into their new stadium.
Spurs are now generating more money than any other club in London, with Chelsea in ninth overall and Arsenal in eleventh place out of the top ten as the season in a row is unsuccessful for the Champions League.
The Ronaldo effect
The Deloitte study does not include income from player transfer fees. The top 20 had record sales of £ 8.2bn in 2018/19, an 11% increase over the previous year.
Only Olympique Lyonnais (17th) and SSC Napoli (20th) entered the top 20 after the 2018/19 season.
Italian champions Juventus returned to the top 10 and Deloitte said that the arrival of Real Madrid striker Cristiano Ronaldo "increased Juventus' commercial appeal".
Ronaldo has more Instagram followers than Real Madrid and Barcelona combined.
"As a result, Juve saw an increase in commercial revenue, due in part to increased brand visibility in 2018/19," said Deloitte. "The club also increased revenue from sales of goods following the signing of the marquee."