Real top the table for the third successive year, as their revenue increased by 20 per cent to 236 million pounds (464.8m dollars), but United showed a bigger per centage rise to climb two places to second on 212 million pounds.
Barcelona, Chelsea and Arsenal are third, fourth and fifth, but with the new Premier League television deal taking effect, English clubs are well placed to force themselves even higher.
"Real Madrid are still at the top after an impressive 20 per-cent growth in revenue, but Manchester United closed the gap and have the potential to catch Real up and take that top spot possibly next season or the season thereafter," said Paul Rawnsley, director of Deloitte's sports business group.
"To some extent, that will depend on how they perform relative to Real Madrid in the Champions League."
Three other English clubs - Liverpool (eighth), Tottenham (11th) and Newcastle (14th) - are also in the top 20, with Celtic in 17th.
"We would expect to see as many as 10 of the top 20 being made up by English Premier League clubs in next year's table," Rawnsley said.
"There are different ways of measuring the health and quality of the league, but there has been period of strong financial growth in terms of broadcasting rights and matchday and commercial revenues.
"Yes, the clubs spend a lot of money on wages, but overall, the Premier League clubs are profitable."