The Brewers designated Gasser as the 27th man for Tuesday's doubleheader against the Cardinals, and he's scheduled to start Game 2.
The left-hander was optioned to the minors last week, but the expectation was he would rejoin the big club to pitch in Tuesday's twin bill. Gasser has a 4.54 ERA, 1.29 WHIP and 36:13 K:BB across 35.2 innings (seven starts) in the majors this season, though he's been more effective in his past three outings with a 2.60 ERA and 0.98 WHIP.