Outgoing Celtic manager Ronny Deila and his assistant John Collins with the SPL trophy at Celtic Park on Sunday Picture by PAJohn Collins has told Celtic they can only consider cashing in on key duo Arne Engels and Alistair Johnston after their Champions League play-off and if they have adequate replacements lined up. “It’s always a challenge, selling good, established players and bringing in new talent,” said Collins, promoting Premier Sports’ coverage of Scottish football. The day they leave, the replacement’s in, or the replacement’s in before they leave. “It’s not as easy as it sounds but I’d like to think Celtic won’t be selling any of them before the Champions League qualifier. “If you ask any Celtic fan, they want to be with the big guns in the Champions League.