The Washington Nationals placed right-hander Trevor Williams on the 15-day injured list Tuesday with a right flexor muscle strain.
Williams, 32, had been scheduled to start Tuesday's game against the visiting New York Mets.
He is 5-0 with a 2.22 ERA this season, allowing two earned runs or fewer in nine of his 11 starts.
The Nationals called up left-hander DJ Herz from Triple-A Rochester to start in his major league debut.
Herz, 23, is 3-2 with a 3.75 ERA in nine starts this season at Rochester. He struck out 42 batters and walked 29 in 36 innings.
Williams owns a career record of 49-54 with a 4.34 ERA in 200 games (159 starts) with the Pittsburgh Pirates (2016-20), Chicago Cubs (2021), Mets (2021-22) and Nationals.