Mikolas will undergo surgery on his right flexor tendon and will miss the remainder of the season, Derrick Goold of the St. Louis Post-Dispatch reports.
Mikolas' forearm issues date back to the end of last season, though he was able to throw throughout summer camp. Notably, the procedure he'll undergo is not Tommy John surgery, so he won't be forced to miss the entirety of the 2021 campaign as well. He's expected to be ready for the start of next season. Daniel Ponce de Leon will take his place in the rotation and will start Wednesday against the Twins.