Astros manager Joe Espada said Sunday that an MRI on Bloss's right shoulder revealed inflammation, Chandler Rome of The Athletic reports.
The 23-year-old right-hander was placed on the 15-day injured list Saturday and will refrain from throwing for at least a few days until the swelling subsides. He sustained the injury in his major-league debut against the Orioles on Friday, when he was removed after giving up two runs on six hits and one walk while striking out two over 3.2 innings.