Long-standing football agent Mel Stein has predicted the transfer market will "plummet to Earth" within the next 10 years.
The transfer window closed on Thursday, with Premier League clubs spending an unprecedented Â£1.4billion during a summer in which Paris St Germain smashed the world record by paying Â£198million for Barcelona's Brazil star Neymar.
Stein, who represented Paul Gascoigne, Chris Waddle and Alan Shearer, is now president of the Association of Football Agents and believes spiralling fees are set for a crash.
"It is galloping away and it is like the house market - when it reached its peak it crashed and this market will crash inevitably," Stein told Radio 5 Live's Sportsweek programme.
"It is unsustainable if you think about it. If you look at the number of players who were jobbed out in this window who clubs had paid Â£20million for and were pleased to get rid of them for Â£3million, Â£4million, Â£5million, having rarely played them, you can't keep that going.
"I think people buy a player and find he is not as good as they thought he was and they realise, 'It's not the money we paid for him, it is the money we are paying on a weekly basis - how do we get him off our wage book?'.
"I know many clubs who were saying they had to get four or five players off their wage book before they could do a deal.
"Eventually the people who own the clubs and put in their own money will get tired of it or their own businesses will come under pressure.
"Something has to give. I am not saying it is going to crash this season or next season but I think there has to be a crash.
"I think I can see this game actually plummeting to Earth sometime in the next 10 years."
Stein, 72, also criticised clubs for selling on young players only to buy them back at inflated prices. One recent example saw Manchester United last summer pay Juventus Â£89million for Paul Pogba, a midfielder who had previously been at Old Trafford.
"Clubs buying back players they have already sold is not irrational, it is pure embarrassment," Stein added.