Lopez is scheduled to start Friday's game vs. Rays. The 23-year-old has been on the disabled list since Aug. 19 with a strained back. Lopez is 0-1 with a 6.97 ERA and 12 strikeouts in two starts with the White Sox this season.
Fulmer, who is the organization's No. 11-ranked prospect according to MLBPipeline.com, made his first Major League start on Aug. 21 against the Twins, allowing six runs on four hits and three walks over 1 1/3 innings for the loss. Fulmer was 7-9 with a 5.79 ERA and 96 strikeouts in 126 innings over 25 starts with Charlotte this season.
Holmberg is 2-3 with a 3.55 ERA and 28 strikeouts in 50 2/3 innings with the White Sox this season.