The 30 year old, who plays MCKinley High graduate Finn on the hit show, voluntarily enrolled in a treatment programme to address "substance addiction" issues and as a result, he will miss out on shooting for the final installments of season four.
The absence of his character will be explained to viewers as part of the storyline, according to Deadline.com.
However, Tv bosses claim they will stand by Monteith as he battles his personal demons and insist he will remain a part of the series.
A statement issued by executives at 20th Century Fox Tv, the company behind Glee, reads, "Cory is a beloved member of the Glee family and we fully support his decision to seek treatment. Everyone at the show wishes him well and looks forward to his return."
Co-creator Ryan Murphy also reached out to Monteith via Twitter.com on Monday (01Apr13), writing in a post, "I am so proud of Cory Monteith and love and support him 100 per cent", while the actor's co-star Amber Riley tweets: "I support you big bro, love you to life (sic). So proud of you @CoryMonteith get well soon".