Matthew Morrison thinks Glee had been in decline for several seasons.
The 36-year-old actor - who played teacher Will Schuester in the musical drama series - has criticised the programme for having a large cast with characters that the audience didn't connect with.
He said: "Glee had its heyday, and then it kind of just slowly started declining. There were just so many characters. There are a lot of people and a lot of story lines. It's one of the biggest casts on television.
"They have the New Directions, the original New Directions, and then you have the new New Directions ... The new ones didn't really click with people, so they had to start bringing back in the old people."
Of the show's Friday night slot, he added: "It's where shows go to die."
And Matthew - who was unsure of the air date of the show finale - claimed the plot lines became "confusing" with various strands forgotten.
He told New York magazine: "They have so many things that we don't even talk about. Sue having a child. We're always like ... I forget the baby's name right now. Where's Wanda, or whatever its name is?"
Jane Lynch, who played cheerleading coach Sue Sylvester, echoed his comments.
She said: "It's like emotional whiplash, my character. I have that redemption scene with Matt: 'I want to be your friend, I'm jealous of you.' I had that scene six times."