Johnston & Engels can't leave before play-off - Collins

John Collins says Celtic must not cash in on key duo Alistair Johnston and Arne Engels until after their Champions League play-off. Martin O'Neill's side face LASK in Europe later this month, having failed at the same stage against Kazakh side Kairat Almaty last term. Canada right-back Johnston is wanted by Everton, while Celtic have turned down a bid from West Ham for Belgium midfielder Engels. Celtic's recruitment strategy has come under question in recent seasons after Kyogo Furuhashi, Adam Idah and Nicolas Kuhn were all sold, with their replacements largely flattering to deceive. And the club's former midfielder Collins says Celtic must have adequate replacements lined up if Johnston and Engels are allowed to leave this summer. "It's always a challenge, selling good, established players and bringing in new talent," Collins said. "It's nothing new, that's the merry-go-round that all the clubs have. You sign young players, you develop them, the big boys from England come with the big money and tempt the players and ultimately you end up selling them for top dollar and you've got to replace them. "The secret is, you have the replacement lined up. 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. I think that would be a risk. "If you ask any Celtic fan, they want to be with the big guns in the Champions League. They never got it last year. "It was bitterly disappointing to go out against a weak team, so hopefully they can keep those key players that the big boys are after, get the result, get through and then if they have to sell them, they get good offers after that, and hopefully Celtic have had the time… "I think everybody knew there was every chance there were going to be offers coming in for those two players, so they've had time to look for replacements." Celtic have made just two summer signings so far - spending significant money on attacking duo Kasper Hogh and Camilo Duran. "I'm happy with the two forward players they've brought in, but they're still needing to strengthen the squad, there's no doubt about that," Collins added. "I'd like to see another midfielder with energy and legs, and I'd like to see another winger in, and maybe another centre-half. I think they definitely need to strengthen all over the pitch."