Kopech, 22, was originally a first-round draft pick (No. 33 overall) by the Boston Red Sox in 2014.
The White Sox acquired Kopech in December 2016, along with Yoan Moncada, Luis Alexander Basabe and Victor Diaz, in exchange for Chris Sale.
ESPN.com's Keith Law had Kopech as the No. 9 overall prospect in MLB when he updated his rankings in July, writing there is "[Noah] Syndergaard-Justin Verlander upside" if he can find more consistency with his off-speed pitches and improve his control.
In 24 starts at Triple-A Charlotte this season, Kopech has a 3.70 ERA with 170 strikeouts, 101 hits allowed and 60 walks in 126.1 innings.