Cory Monteith's rehab stint came ''out of the blue'' for Matthew Morrison.

Cory checked out of a treatment facility at the end of April after a month-long stay to recover from substance abuse and his 'Glee' co-star admits he was surprised when he learnt of his friend's troubles, as he is always totally ''professional'' on the set of the show.

Matthew, 34, exclusively told BANG Showbiz: ''The thing is, it's funny because it kind of came out of the blue - I had no idea. He's so professional at work, he always shows up and knows his lines; he's great at work so you would never really know.''

Despite having no contact with Cory during his treatment, Matthew ''prayed'' for him and is ready to support him in anyway he can when the 30-year-old actor returns back to work on the next series of the programme.

Matthew - whose latest album 'Where It All Began' is released in the UK on June 17 and is available on Amazon pre-order now - added: ''It's hard to support because they're kind of locked away with no phone or anything, you can't really reach out to them.

''But silently we support them and we pray for them and that's such a thing where he has no control over it. It's an addiction, it's a problem and so I'm happy to help him.''

Cory - who had remained clean since he was 19, when he last checked into rehab - and his on-screen and real life girlfriend Lea Michele have been on vacation since he finished his treatment programme. The pair are currently in Mexico to ''rest up''.