Until breaking a bone in his foot last Saturday, against Nottingham Panthers, the defenceman was one of only five skaters to have been ever-presents in the squad.
He'd joined Josh Pitt, Tanner Eberle, Jonathan Phillips and Ryan Martinelli in the 'always-available' set.
Steelers managed without him in the away win at Coventry Blaze last Sunday and will be without him tomorrow night at Nottingham and for the rest of the league programme, it seems.
That could damage Sheffield's power play in particular, where he and Ben O'Connor are chief architects, roaming from deep.
In fact, Matheson is the team's joint power play top-scorer, alongside Pitt.
But such is the nature of the foot injury, the 35-year-old Canadian might not be back at all this season, depending whether Sheffield make the later stages of the playoffs.
Steelers may yet sign a replacement d-man before the transfer deadline is up - but he won't play this weekend at Nottingham or Coventry Blaze on Sunday.