But for bit-part player Killen, that was the moment when "the writing was on the wall" as far as his own future was concerned.
He said in the Daily Record: "I think what he said did upset a lot of the players, if we're being honest about it. And, yes, the feeling at the training ground lately has been a bit confused.
"But that's fine. We're all professional football players and we realise that this is what happens when a new man takes over. He comes in with his own ideas and his own plans for the club. He wants to bring his own men and that's his prerogative.
"Maybe he was trying to ruffle a few feathers by what he said. Maybe he was looking to get a positive response out of the guys who were there. Sometimes a manager needs to say certain things in order to get a reaction and maybe that's what he was trying to do.
"Did it backfire? Well, I wouldn't like to say."
New Zealand striker Killen was one of four players to leave Parkhead yesterday, with Barry Robson and Willo Flood joining him at Middlesbrough and Gary Caldwell going to Wigan.
Killen insisted he was reluctant to "throw in the towel", but added: "With the World Cup this summer, I knew I had to do something to get myself some game time and that's why I'm so delighted this opportunity has come up.
"Of course there is a concern that I might end up moving down here swapping once bench for another. I'd be lying if I said that thought hadn't crossed my mind.
"But I still think I'll have a better chance of playing football here than I would have had at Celtic."