Lopez hasn't pitched since Saturday while managing a back injury, Vinnie Duber of AllCHGO.com reports.
Lopez surrendered a run over one-third of an inning and was charged with a blown save Saturday, though it's unclear if that's when the back issue first surfaced. The White Sox have a scheduled day off Thursday, and it's unclear if the 31-year-old, who has a 3.61 ERA across 77.1 innings this year, will be available Friday versus the A's.