Schalke sporting executive Christian Heidel said he has grown annoyed by English agents offering their players to the club, saying they "bug you from morning to night."
The transfer window closed in England on Aug. 9, and with the German deadline on Aug. 31, Schalke have been linked in recent weeks with loans for England internationals Danny Rose, Danny Drinkwater and Ruben Loftus-Cheek.
Heidel, who said the club would not sign those three players, said the different deadlines mean clubs and agents are now hoping to get their surplus players onto the European mainland.
"The English agents currently bug you from morning to night because probably they have 100 players to give away in England," Heidel told Deutschlandfunk. "They sometimes have 30 to 40 players in the squad, and you can see how difficult it is for the English to offload their fringe players."
Heidel, who hired Liverpool's Jurgen Klopp as coach during their time at Mainz, said he has the impression "a bubble is building in England."
"The squads get bigger and bigger," he said. "They might even have to build new stands, just for the players who don't make the matchday squad.
"You could argue the money's there, but the question is, if someone's in the stands for six months, can you offload him in the winter or next summer? And they'll buy new players again in the summer. This can lead to a bubble."
Elsewhere, Dortmund sporting director Michael Zorc said he believes the top European leagues will synchronise their transfer windows again.
Zorc told kicker that the new Champions League system, with four guaranteed places for Spain, Germany, England and Italy, curtailed the need for the late-August deadline.
"I was an advocate for the end of the window on Aug. 31. There were playoffs for the Champions League. And it's not unimportant to know in which competition you play, also from an economical point of view," Zorc said.
"I see things a bit different now. In the end, it will lead to a corresponding transfer window for at least the big leagues."