There have been various reports about why that may be, but - even in the widely reported story of a training ground bust-up, carried by the Daily Mail - it began with Colback training away from the first team.
He featured recently for Peter Beardsley's reserve team and that appears to be his home, for the timebeing at least.
If Benitez had already decided to dispense of Colback before any alleged feud, that would suggest he does not feel the former Sunderland man's talents befit the team he is looking to build this season.
And that's a perfectly understandable stance given Colback's role last season and how differently Newcastle plan to play.
In the Championship, Benitez's men bossed games and Colback was almost an insurance policy, ready in the midfield to snap into action and commit a niggly foul if it looked like the opposition were breaking.
Under Benitez, Colback has never been a ball-playing midfielder or an energetic box-to-box presence - nor has he been particularly disciplined.
This term, as Newcastle sit back, soak up pressure and look to counter themselves, there simply is no room for such a player.
Colback, even with his limitations, had a function last year. It may well be that Benitez quickly realised that would not be the case back in the Premier League.