Borussia Dortmund coach Thomas Tuchel says the escalation of the transfer market is "crazy" and risks alienating supporters.
Dortmund are reported to have broken their own transfer record when signing Andre Schurrle from Wolfsburg for a fee said to be around €30 million this summer, while Mario Gotze has returned from Bayern Munich for an initial €22m, but those fees pale in comparison to the sums being paid elsewhere in Europe.
Juventus signed Gonzalo Higuain from Napoli for €90m this week, and they could receive a world-record €120m if Paul Pogba completes a transfer to Manchester United.
Tuchel, 42, feels the high fees could damage the relationship with fans.
"The market is crazy," he told a news conference on Thursday in Shenzhen, China. "Prices are out of control in my opinion, and it's not healthy, because there it has no relation anymore to the people who come to the stadium and watch the game.
"We have to be careful not to lose it [the relationship with fans]. If it's only about ego, if it's only about money, then we lose it. The game is for the people.
"As with any subject, if there is too much money in circulation, it's only a question of time until it gets out of control and blows itself up."
Borussia Dortmund have sold Henrikh Mkhitaryan, Ilkay Gundogan and Mats Hummels this summer for over €100m in total. All three had one year left on their contracts.
Overall, the club has invested more than €110m on eight new signings.
"It is what it is, but we keep our feet on the ground and do it our way," he said.
Dortmund goalkeeper Roman Weidenfeller, 35, agreed with Tuchel's assessment.
"It has been often discussed whether a ceiling will be reached at some point, but the current trend shows that there are no limits in football," Weidenfeller told Sky Sports.
"It's a pity that contracts are not adhered to anymore. They don't count for much. Football is becoming more selfish, which is sad considering that it's still a team sport."
Weidenfeller joined BVB in 2003 as a free agent and is currently under contract until next summer.