"If we need to adjust because of innings load at some point or whatever reason, we will," Hahn said of the No. 59 prospect in all of baseball per MLBPipeline.com. "But as I've said several times, we didn't want to bring anyone here until we felt they were going to get the ball every fifth day and be part of a normal starter's routine."
Lopez, 23, was acquired from the Nationals in December as part of the four-player Adam Eaton deal. Lopez basically has forced the callup with 63 strikeouts over his past 46 2/3 innings for the Knights, allowing 14 earned runs over that stretch.
But it was more than just numbers that convinced Hahn.
"More consistency with the fastball, he threw quality strikes, trusting his off-speed pitches, being able to throw any pitch in any count," Hahn said of the proverbial boxes checked by Lopez. "Taking the ball every fifth day and being prepared for that specific outing. The work that's done in between starts, some of the stuff that's not publicly seen. He's done everything we've asked of him, and now's the time for him to take that next step."
"Everybody has been looking forward to seeing some of the guys that have been gliding through the system," White Sox manager Rick Renteria said. "Last four or five outings have been really, really good. Everybody in the city and obviously the club has been looking forward to starting to transition some of those guys who are ready to check off a few of those boxes and be able perform for us and we're looking forward to having him here."
Lucas Giolito also is a possibility for a September callup, as is Carson Fulmer and Tyler Danish. So a six-man rotation might come about in September per Hahn.
"There still will be some development that occurs here in Chicago," Hahn said. "In the end, that last stage of development has to happen at the big league level where the speed of the game is a little quicker and the hitters are a little bit more advanced. I look forward to seeing how he responds to that challenge."
With an off-day Monday, the White Sox will be able to skip Lopez for the two-game set against the Dodgers in Los Angeles and potentially have him open the ensuing series at Texas.
Scott Merkin has covered the White Sox for MLB.com since 2003. Read his blog, Merk's Works, follow him on Twitter @scottmerkin, on Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.