The Red Sox have placed Justin Masterson on the 15-day disabled list, calling up Robbie Ross Jr. to take his place on the roster.
The official reason for Masterson's trip is "right shoulder tendonitis," which is actually slightly more specific than might have been expected given John Farrell's vague statements that something was "not right" with him. It's possible that this is a real reason for Masterson's ineffectiveness, and in particular his inability to hit so much as 90 MPH with his fastball.
Importantly, though, if that's the case, then Masterson will be able to prove it. And he'll be able to prove it before he takes the mound for another major league inning. If Masterson is just slightly injured rather than more seriously broken, and time on the disabled list is enough to fix that, then he can show it with increased velocity in rehab starts.
At this point, though, that seems like something of a long shot. And as a pitcher who has never really commanded the strike zone with any great authority, Masterson can't get by without that extra heat. Normally when a player goes on the disabled list, there's a spot waiting for their return, with the occupant in the interim understood to be entirely temporary. That can't be the case here. Masterson has to prove himself worthy of that spot by showing the Red Sox something he hasn't yet this year.
Otherwise, whether it's Steven Wright, Eduardo Rodriguez, Brian Johnson, or any other arm that has even the slightest chance of success against major league hitters, the replacement shouldn't be seen as a temporary appointment. Whoever gets the start this week and in the weeks to come, Justin Masterson should no longer hold any claim to that roster spot. He's at the back of the line, and should have to prove he deserves to be anywhere else.
If, indeed, Steven Wright is in line for the start on Sunday, then Robbie Ross' addition to the roster should go relatively smoothly. Wright was tagged as a long relief arm before this, so the move would be one bullpen arm to the rotation, one Triple-A arm to the bullpen. No additional shifts required.