The Athletics recalled Lopez from Triple-A Las Vegas on Tuesday.
The left-hander was a rotation piece for the A's early this season, but he was optioned to Triple-A in early June after posting a 6.75 ERA, 1.84 WHIP and 38:33 K:BB across 50.1 innings. Lopez struggled in his first two starts with Las Vegas but rebounded by allowing just one run across 11.1 frames in his last two outings. He's likely to be available out of the bullpen, at least initially.