Miles Mikolas will have season-ending surgery to repair a tendon in his strained right forearm.
The St. Louis Cardinals placed the right-hander on the 10-day injured list before Tuesday's game.
Mikolas, 31, pitched four innings in an exhibition game last week. He missed spring training because of the injury, but after nearly four more months to rest during the coronavirus shutdown, he ramped up his activity when camp reconvened.
He was 27-18 with a 3.46 ERA in 64 starts the past two seasons.