Kopech will miss the entire 2019 season and is "expected to be ready for spring training in 2020."
Tommy John surgery has been recommended for the 22-year-old, but plans have not been finalized since he is scheduled to receive a second opinion in the coming days.
"It sucks," Kopech said, according to MLB.com's Scott Merkin. "That's it. It sucks."
The fireball-throwing right-hander made his highly anticipated Major League debut against the Minnesota Twins on Aug. 21, and he didn't disappoint. Despite only lasting two innings, the 2014 first-round pick logged four strikeouts and no walks while flashing his exceptional velocity.
However, his season ended on a sour note Wednesday when he was shelled to the tune of seven earned runs, including four home runs, across 3.1 innings against the Tigers.
Kopech finished his first stint in the majors 1-1 with a 5.02 ERA, 15 strikeouts and two walks.