Kolarek was optioned to Triple-A Las Vegas on Sunday, Matt Kawahara of the San Francisco Chronicle reports.
Kolarek was promoted from Triple-A during the opening weekend of the season, and he'll return there after giving up four runs over his past three outings. Overall this season the left-hander has a 4.58 ERA, 1.58 WHIP and 9:8 K:BB across 17.2 innings.