Royals prospect Kyle Zimmer remains in extended spring training after ‘arm fatigue’

As the Royals broke camp last week and assigned players to their minor-league affiliates, one name was conspicuously absent from a roster: Top pitching prospect Kyle Zimmer remains in extended spring training after experiencing some “arm fatigue,” assistant general manager J.J. Picollo told The Star.

Zimmer is expected to continue throwing side sessions in a controlled environment as club officials inspect his progress. Picollo said there was no specific timetable for his departure from the Royals’ complex in Surprise, Ariz.

“He’s truly day to day,” Picollo told The Star in a text message. “As long as he’s comfortable, we will move him forward but it’s tough to put a time frame on it.”

The source of the issue is Zimmer’s shoulder, which caused some fatigue and resulted in his pace being “slowed up,” Picollo said. Zimmer allowed one earned run in six innings over three appearances at big-league spring training. He was optioned to Class AAA Omaha on March 14 as part of a flurry of other roster moves, and he finished the spring in minor-league camp.

The Royals were hopeful that Zimmer could begin the season in the starting rotation at Omaha. For now, that plan is on hold. For Zimmer, 24, it is a minor setback but also a vexing one. Since being drafted with the No. 5 overall pick in the 2012 draft, Zimmer has been beset by injuries. He underwent an elbow cleanout after the 2012 season. He strained his latissimus dorsi muscle in May 2014 and pitched only 4  2/3 innings that season. After the 2014 season, he underwent a minor shoulder operation to remove damaged tissue from his rotator cuff.

But Zimmer finished the 2015 season with a clean bill of health and arrived at spring training in an optimistic mood. Club officials hoped Zimmer would position himself for an arrival in Kansas City at some point in 2016. His ceiling remains among the highest of all pitchers in the Royals organization. For now, Picollo said, the Royals will take it slow.

The club “decided to be cautious early,” Picollo said.

This story was originally published April 6, 2016 at 1:10 PM.