Manchester United are expected to become world football’s biggest earners in the next 12 months.
Real Madrid topped Deloitte’s Football Money League for the 11th consecutive year, generating 577m euro (£439m) in 2014-15.
Champions League winners Barcelona are second with 560.8m euro (£426.6m), with United third on 519.5m euro (£395.2m).
But Deloitte said there was a “strong possibility” United would overtake the La Liga sides in next year’s edition.
Deloitte is a professional services firm, whose sports business group produces an annual table of the clubs with the highest revenues.
The combined revenue for the top 20 clubs in the table rose by 8% from last year to 6.6bn euro (£5.08m), a new record.
Manchester United, who failed to qualify for either Champions League or Europa League last season, slipped from second to third following a year-on-year drop in revenue.
However, Deloitte said their “strong commercial growth” and “ability to agree impressive new sponsorship deals”, such as the £75m-a-year Adidas kit agreement, compensated for a lack of European football.
With the new £5.1bn television rights deal starting from 2016-17 season, Real Madrid would come “under increasing pressure” next season and in future years, added Deloitte.
The wealth of the Premier League – mainly due to strong broadcasting deals – means 17 Premier League clubs feature in the top 30.
West Ham make the top 20 for the first time since 2005-06 with revenues of 160.9m euro (£122.4m), more than Turkey’s top club, Galatasaray.