John's not the only one who's having what he's worked for threatened. He's definitely not the only one feeling... territorial, and he's sure as hell not the only one who's pissed off about it.
He nods to Johnny, terse but still indicating that he's heard and understood.
Then his attention is down to John, eyes fixing on the younger man's and his expression is intense. "I suggest," he snaps, voice low, cold and dangerous, "that you concern yourself with your own safety, Mister Barrowman, and leave the running of the club to those who pay your staff."
It's not much of an overt threat, but he can and will make it more explicit if he has to. Mostly it's a reminder that John is an employee. For the moment.