The Brewers placed Koenig on the 15-day injured list Monday with a left elbow sprain.
The left-hander has been diagnosed with UCL damage but will attempt to rehab the injury, per Curt Hogg of the Milwaukee Journal Sentinel. He's expected to miss 2-to-4 weeks. Koenig has been a valuable piece out of the Milwaukee bullpen since 2024, posting a 2.62 ERA and 24.7 percent strikeout rate. His spot on the roster and in the bullpen will be filled by Shane Drohan, who was recalled from Triple-A Nashville.