He said: "What to expect? I don't know if I can give away too much, but there will be a lot of people graduating at the end of the season.
"I'm not sure what that's going to mean for the show, we're probably going to get a lot of new members and maybe some of the old 'Glee' members will become student teachers of mine, I don't know."
Matthew also thinks many people will have been "surprised" when they saw his character Will finally in a relationship with germ-phobic teacher Emma.
He said in a video for internet search engine site Bing: "It's my favourite season so far. I think the coolest thing is that for Will's character is he's in a great relationship with Emma, you know the first episode you see him rolling over in his bed and she's there living with him now. I think that was a big surprise for people."