Bummer was recalled from Triple-A Charlotte on Saturday.
Bummer last saw the majors in early June and had a solid 3.26 ERA and 21:6 K:BB over 19.1 innings. The 24-year-old did allow a .321 opponent batting average and a 1.71 WHIP, which suggests some regression is likely in order. The 24-year-old could be used as a situational left-hander for the White Sox.