Falchuk said that characters on the Fox musical facing a long-distance romance after last season's graduation will find staying together a "pretty tough challenge".
"Long-distance relationships are hard," he told TV Line. "They're not impossible, but they're really hard. And with all the couples, we're really trying to look at what it takes to have a relationship when one person leaves.
"It's particularly hard when somebody graduates high school and someone is still in high school. The second you graduate high school you're in a different world. You see things differently, your needs are different, your perspective on things is different. So I think it's a pretty tough challenge."
Falchuk's comments come after Glee creator Ryan Murphy teased on Twitter last week that some of the "core relationships" of the show will come to an end in season four, highlighting Kurt and Blaine, Santana and Brittany and Will and Emma as those in danger.
"I'm not going to say who breaks up and who doesn't, but they all... get kicked in the nuts," he wrote. "And it's all about how do they recover - and can they recover?
"And some don't. Absolutely some don't. Of those couples, not all of them are going to make it. It's like Titanic."
Glee will return to Fox on September 13 on Fox. In the UK, the series airs on Sky1.
Watch a promo for Glee season four below: