"It is not a particularly good thing for clubs of our size, and certainly not for clubs outside the Premiership who need to raise cash during the season," says the Hammers boss.
"It is possible that one of these clubs could go out of business because they would have to wait to sell someone."
The possibility of a transfer window in England is currently being discussed, and it would include loan transfers as well.
Glenn adds: "It doesn't help us because if we want to loan a player, and a loan constitutes a transfer, he can't then go back to his club during the season because it would be seen as two transfers.
"We want to use the loan system. If two or even three quality players come up that could go straight into the first team I would definitely take them until the end of the season to play because we haven't got any strength in depth."
Glenn is still looking to strengthen, and he adds: "Everyone needs a little bit of luck when you sign a player; even when you have seen him play well at another club there is always an element of a gamble that he might not settle in.
"But generally speaking, if you have got confidence in your ability to judge a player you should get it right more often than not.
"No matter how careful you are you will get the odd signing that doesn't come up to scratch - but it should be the odd signing, not five or six."