Garza, 7-7 with a 3.58 ERA, left Sunday's game against St. Louis after allowing just one hit in six shutout innings. The move was retroactive to Aug. 4.
''We'll look at it like it is just going to be the 15 days, but we'll determine that as we go on,'' Brewers manager Ron Roenicke said. ''He won't pick up a ball or throw it for a while. These things are hard to tell. Obliques sometimes last longer than you think. He says he doesn't think he did it bad. Hopefully that's the case.''
Garza also strained his left oblique in spring training last season with the Cubs and missed seven weeks. He said Tuesday he didn't think this injury was as severe.
''It's more precautionary than anything,'' Garza said. ''Really don't know a time frame or anything. Just didn't want to surprise anybody if I couldn't go in five. It's more of their call, not mine. It's, once again, a waiting game. That's it.''
In his last three starts, Garza has allowed two earned runs in 21 innings.
Reliever Rob Wooten was called up from Triple-A Nashville to fill the roster spot.
Wooten is making his third appearance this season with the Brewers. He is 1-4 with a 4.36 ERA in 37 games.