Pirates Prospects is reporting (sub. req’d) that Joe Musgrove was shut down due to right shoulder discomfort. The severity remains to be determined. Musgrove went on the disabled list last season with a sore shoulder, but returned after two weeks, so it’s not a certainty that this is a significant issue.
UPDATE: As Pedropower notes in the comments, Adam Berry is saying on twitter (I’m using a phone and can’t link it) that Musgrove has said it’s just a precaution and not serious.