O'Reilly was sacked when the series was moved to Sunday evenings on BBC1 and she went on to successfully sue the BBC for age discrimination.
The programme relaunched with younger presenters Julia Bradbury and Matt Baker, along with veteran broadcaster Craven.
Craven, 73, told Radio Times magazine: "It got very unpleasant and for the team it was an unhappy time.
"I didn't get involved because I'm not management, I'm just a hired hand.
"When you're in the front line as a presenter, the easiest thing for a new manager to do when they come in is get rid of you and bring in a new face and that's always been the case. I'm incredibly lucky because I've survived about 12 different series producers on Countryfile."
Asked whether O'Reilly was right to sue the corporation, Craven replied: "Yes, if she felt that she'd been badly treated then of course she was right to take them on."
Craven is about to celebrate his 25th anniversary on the show. He said: "I think of myself as very much a country person."