But Zimmer, who has a history of arm and shoulder issues, said his health is fine.
"There's no injury at all," Zimmer said on Sunday. "There's nothing wrong. This time of year, I don't even look at velocity. I generally just let the hitters tell me how I'm doing, and [on Saturday] I was getting the fastball past guys."
Zimmer, the Royals' No. 2 prospect overall according to MLBPipeline, gave up one hit and struck out one.
"I just judge if I'm getting through the ball," he said. "And I was. I felt like I was finishing.