The show will start off with the news that Finn has died, and follow through with the characters remembering and honouring him. Lea is not expected to appear until the end of the episode.
"Just read Cory Monteith memorial episode," tweeted Jane Lynch, who plays sports coach Sue Sylvester in the show, earlier this week. "Most beautiful thing. Thank you, @MrRPMurphy @BFalchuk Ian Brennan."
The cast of Glee have been working hard to support and comfort each other, and Lea is said to be doing an "amazing" job at holding her co-stars together.
"Lea has been amazing," a source told HollywoodLife. "She is definitely very sad, but has gotten so much better and has really been strong.
"The whole crew and cast are now a family and Lea is leading us all back to a normal set life. Cory was a cool guy and will be missed."
The show's leading lady has been letting fans into her Glee world and thanking them for their love and support following Cory's death from a heroin and alcohol overdose in mid-July.
She has also kept fans in the loop by sharing photos from the set of the hit musical show.