Misiorowski, 24, looked to the dugout and left the mound shortly after throwing a fastball by Washington's James Wood with one out.
His fastball clocked at 98.9 mph, which was his slowest fastball of the night. Earlier in the game, Misiorowski had thrown five straight fastballs that were clocked at at least 102.0 mph, with the top reaching 103.0.
The Brewers' young star pitcher had struck out eight and walked two before heading off, retiring the last 12 batters he faced.
Misiorowski was having a solid season through his six starts on the season heading into Friday. The 2024 rookie All-Star was tossing a 3.31 earned run average with a National League-leading 51 strikeouts this year.