Every staff in baseball has injuries and injury histories. The Twins had been exceedingly healthy in their pitching staff until Pablo's arm injury, now Matthews, whose diagnosis wasn't great, and things don't look so rosy.
We can add in that SWR's start was not confidence inspiring and it's fair to say that the Twins starting staff looks a lot weaker than it did two weeks ago. Guys need to step up and even if they do, cracks are showing in the starting rotation.
Equally important, the bullpen has been very healthy and that is with veterans with long injury histories (Stewart and Topa). Someone said that Alcalá has an option, but that's not really true (can't be optioned without his consent), but Tonkin is on the road to recovery and there are no reported injuries for any relief pitcher on the 40-man roster.