The actor told IGN that he has been worried on more than one occasion that his character Castiel would be written out of the show.
"The show cannot go on without Sam (Jared Padalecki) and Dean (Jensen Ackles), but we have seen that the show had started without me and can go on without me," Collins said. "So, yes, whenever there's a changing of the guard, I have been nervous, not always without cause."
A former series regular, Collins appeared in just five episodes of Supernatural's seventh season, which concluded with Castiel and Dean trapped in Purgatory.
"I thought at the end of last season, 'Hey, thank God they left me in Purgatory with Dean. I'm definitely going to be significant next season'. Then there was a little back and forth where it wasn't really clear whether I was going to come back at all," he explained.
"The way in which I do come back is not at all what I expected. But I'll be back much more significantly this season than last."
The CW president Mark Pedowitz recently confirmed that Collins will appear in a "minimum of eight" new Supernatural episodes.
The series returns to The CW in the US on October 3. In the UK, Supernatural airs on Sky Living.