“Glee” star Cory Monteith may be singing a sad tune — the 30-year-old actor checked himself into rehab this past weekend to treat substance abuse issues. The actor’s rep confirmed the news, saying the star is working hard on his way to recovery, E! News reported.

“Cory Monteith has voluntarily admitted himself into a treatment facility for substance addiction. He graciously asks for your respect and privacy as he takes the necessary steps towards recovery,” said the rep.

Monteith’s girlfriend of one year,  and “Glee” co-star, Lea Michele, 26, tweeted on Sunday that she was "grateful" the struggling star was seeking help; telling People magazine, she plans to stick by Monteith throughout his treatment.

“I love and support Cory and will stand by him through this. I am grateful and proud he made his decision,” she said.

Before entering the unidentified facility, Monteith tweeted on Thursday a cryptic message to his 1.4 million fans.

“Such a beautiful day! Truly seeing the forest for the tree. #gratitude,” he said.

This isn’t Monteith’s first trip to rehab. The actor opened up about his history of substance abuse to Parade magazine in 2011, admitting to frequently skipping school to overload on alcohol and pot as a teen.

“Anything and everything, as much as possible. I had a serious problem,” he said. “I burned a lot of bridges. I was out of control.”

The star admitted that after his first stint in rehab at age 19,  he went right back to his partying ways and resorted to stealing money from family members to pay for his habits.

“I knew I was going to get caught, but I was so desperate I didn’t care. It was a cry for help,” he said, claiming it was a friend who introduced him to acting and that helped him get his life back on track.

“I’m lucky on so many counts -- I’m lucky to be alive,” he said.

A rep from “Glee” said the crew is hoping for a speedy recovery for the actor.

“Cory is beloved member of the “Glee family, and we fully support his decision to seek treatment," the rep said. "Everyone at the show wishes him well and looks forward to his return.”

Monteith has starred on “Glee” as Finn Hudson since the show's premiere in 2009. The actor has two films in post-production that are set to be release in 2013. "All the Wrong Reasons” is a drama about the struggles of four individuals, and “McCanick” is a mystery drama in which Monteith plays a young criminal just released from prison.