The Royals announced that loose bodies were removed from the right-hander's pitching elbow at the University of Kansas Medical Center in Kansas City. He'll miss the rest of this season, but it's not expected to affect his preparation for next year.
"This procedure was anticipated for Kyle upon physical exam during the Draft selection process, so it did not come as a surprise," Royals head athletic trainer Nick Kenney said in a statement. "We feel very good about the outcome, and expect a full recovery in six-to-eight weeks. We do not anticipate this procedure will alter any of Kyle's offseason preparation for the 2013 season."
General manager Dayton Moore said the Royals were aware of the problem prior to drafting Zimmer.
"Going into the Draft, it was documented in some publications that he had loose bodies in there so we knew it, and that at some point in the next six to 12 months that he was probably going to have to have them removed, and our medical team decided it was time to go ahead and get it done," Moore said. "But everything looks good."
Moore said that post-Draft physical examinations showed no ligament damage in the elbow, a crucial point these days for the Royals who have been hit by four Tommy John surgeries this year.
"The film studies we did prior to signing him showed the ligament looked great and the shoulder looked great and that's still the case," Moore said.
Zimmer, 20, pitched with two lower Minor League clubs this season: the AZL Royals in the Rookie classification Arizona League and Kane County in the Class A Midwest League.
He had a combined record of 3-3 with a 2.04 ERA in nine starts, and he compiled 42 strikeouts in 39 2/3 innings against only eight walks. He gave up one home run.
Drafted fifth overall on June 4 out of the University of San Francisco, Zimmer signed three days later for a signing bonus of $3 million.
It's anticipated the surgery will protect that investment.
"Those loose bodies jump around in there and limit his range of motion, so instead of us having to do this in June of next year and he misses a month and a half, let's get it done now so he's ready to go," Moore said.