The Royals announced on Tuesday that Zimmer, who has yet to pitch this season, will be further sidelined with a strained right latissimus dorsi muscle. He won't even begin playing catch again for six to eight weeks or roughly about the All-Star break in mid-July.
"My guess is, it'll more on the side of eight weeks," said J.J. Picollo, assistant general manager-player personnel. "Then he'll start on a throwing program again. Really, he's starting over again -- it's Spring Training again."
The "lat" is one of the largest muscles in the back that relates to the throwing motion, and an injury to the area can cause shoulder pain, although Picollo said Zimmer escaped that.
"If there's a silver lining anywhere, it's not shoulder and it's not elbow so from that perspective we're happy," Picollo said. "It's a large muscle. The bad is that it takes some time to heal, the good is it's not surgery, it's just rest. It could be a lot worse. It'll just test everybody's patience, particularly his."
The news comes one day after the Royals' 22-year-old rookie prize, Yordano Ventura, left a start against the Astros in the third inning with lateral right elbow discomfort.
Zimmer's injury apparently occurred on May 19, when he was pitching in an actual game for the first time at extended spring training in Arizona. He was hoping to start on a trek toward pitching at the Double-A level by the first week of June.
"First inning, his fastball was really good, 94-97 [mph]," Picollo said. "The second inning was good, but the last couple of pitches, his velocity dropped some. He didn't feel a pop or anything like that, just some soreness."
The next couple of days, Zimmer couldn't loosen up.
"It was away from the shoulder area where he's had some problems in the past. It was down in his back and in his lat area, just below his shoulder area," Picollo said.
So Zimmer underwent an MRI which revealed the lat strain.
The Royals have been taking it slow and careful with Zimmer, also 22, for some time now.
The club knew from a pre-Draft physical that he had bone chips in his right elbow, and after he pitched 39 2/3 innings in his first pro summer of 2012, he underwent minor surgery to remove them.
Last year, Zimmer made his way from Class A Wilmington to Double-A Northwest Arkansas, but he made just four starts for the Naturals, with a 1.93 ERA and a 2-1 record, before being shut down in August with biceps tendinitis.
His combined record for Wilmington and Northwest Arkansas was 6-9 with a 4.32 ERA over 22 starts.
Zimmer's strikeout-to-walk ratio was especially impressive in his 18 starts for Wilmington's Blue Rocks. He struck out 113 in 89 2/3 innings against only 31 walks. His record was 4-8 with a 4.82 ERA.
When he began throwing again in December, Zimmer's arm didn't feel quite right, and his entire schedule was pushed back. In Spring Training camp with the Major League club, Zimmer didn't pitch an inning and stayed in Surprise, Ariz., to continue his training program.
"Really, the whole thought process this year was go slow with him ... with the expectation that he'd be able to help our club at some point later this year and be fresh for September," Picollo said. "So that's why we moved the calendar around the way we did."
If Zimmer heals quickly, there could be a chance he could pitch before the Minor League season ends.
"The Minor League season is going to be hard, and it's really hard to say he's going to pitch in the Major Leagues. ... If he's able to come back and pitch a little bit in the Minor League season, I guess we'd reassess it," Picollo said.
When the Royals signed Zimmer for $3 million just three days after he was drafted, they cited the relative freshness of his arm as a plus, because he'd been a full-time pitcher for just two years at the University of San Francisco. He had been recruited by the Dons as a third baseman.
Getting use of that fresh arm has become a continuing problem.
"It's frustrating and I feel for the kid, because he's been in Arizona, going on six months, anxious to get out and play," Picollo said. "Now he's going to have to wait a little longer."