The Brewers placed Koenig on the 15-day injured list Saturday with left forearm tendinitis.
Koenig threw 1.1 scoreless innings and struck out three batters during his appearance Friday versus the Cubs, but he seems to have come away from his outing with an injury. The 30-year-old southpaw has been one of the Brewers' more surprising finds of the season, posting a 1.66 ERA and 1.00 WHIP through 38 innings. Rob Zastryzny was selected from Triple-A Nashville to replenish Milwaukee's bullpen depth.