Premier League clubs' wage bill rose by 15% to £2.9bn in the 2017-18 season, hitting profits - despite them making record revenue during the campaign.
Having five teams each reaching at least the last 16 of the Champions League helped push revenue to £4.8bn, according to analysis from Deloitte.
But the high transfer fees paid out by clubs also helped push up wages.
That brought profit before tax down to about £400m for the clubs, a reduction from about £500m a year earlier.
Tim Bridge, a director in the Sports Business Group at Deloitte, said: "The increased wage expenditure was expected given the busy transfer market in the 2017-18 season, with two record transfer windows driving estimated Premier League gross spend of £1.9bn."
However, he said, broadcast fees are only likely to rise by a small amount in the next three years.
"With the emphasis now on clubs to generate revenue growth from sources other than central broadcast distributions, it may be that we see the levels of pre-tax profit diminish over the next few years," he said.
The "big six" clubs of Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham accounted for 89% of the league's pre-tax profits, according to financial data firm Vysyble.
They earned more than £53.4m a week between them, up from £48.4m the previous season, while the other 14 sides made a combined £39.4m a week, down £200,000 on the year before.
Premier League clubs paid out more than £260m to football agents in the 12 months to the end of January 2019, an increase of £49m on the previous year, according to documents released by the Football Association.
Liverpool were the highest-spending club in the top flight, paying £43m to agents in that period.
Chelsea (£26m) and Manchester City (£24m) were the next biggest spenders.
Fees to agents went up despite spending on transfers falling by more than £500m when compared with the previous season.
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