The Chicago Cubs placed Keegan Thompson on the 15-day injured list and recalled fellow right-hander Anderson Espinoza from Triple-A Iowa on Saturday.
The Cubs did not specify the injury for Thompson, but he reportedly has tightness in his lower back.
Thompson started the Cubs' 8-7 win over the Milwaukee Brewers on Friday night and gave up five runs in 3 2/3 innings. His 104 1/3 innings pitched are the most he's thrown since 2018 in the minors.
After the game, manager David Ross expressed concern.
"I think he's got some fatigue probably setting in," Ross said. "We'll take a big-picture look at that and make sure everything's on the up and up with him health-wise."
On the season, Thompson is 9-5 with a 3.97 ERA. The 27-year-old has appeared in 25 games (17 starts).
Espinoza, 24, is 0-2 with a 4.11 ERA over 15 1/3 innings in six games with the Cubs this season. He made his MLB debut on May 30.
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