Bass was unavailable for Sunday's doubleheader against the Rays due to back tightness, Ben Nicholson-Smith of Sportsnet.ca reports.
Bass tossed a scoreless inning with one strikeout in Friday's series opener against the Blue Jays, but he apparently suffered a back issue that prevented him from entering either of the contests in Sunday's twin bill. It's unclear whether the issue will impact his availability going forward. Bass has converted on three of his four save opportunities to begin the season while also posting a 3.38 ERA and 0.75 WHIP over eight innings.