Monteith, who plays Finn in the show, told TV Guide that the cast is currently working on two new instalments.
He said: "One, 'Born This Way', is a classic Glee episode where we explore embracing the things about ourselves that we don't like and tailoring our performances around that."
Monteith hinted that the episode may have something to do with Karofsky's sexuality and added: "There's a little blackmail involved. It gets kind of heavy."
Monteith explained that the group is also working on an instalment called 'Night Of Neglect'.
"[It's] an episode focusing on artists that may have been neglected or underappreciated over the years," he said. "We were trying to clear a Bjork song, but they couldn't track her down. Apparently she doesn't have a phone number."
Glee airs on Tuesday at 8/7c on Fox in the US and on Monday at 9pm on E4 in the UK.