Chacin has an injury to his pectoral minor muscle involving a nerve entrapment. There’s no structural damage to his biceps, shoulder or elbow. This can be addressed through mobilization and strengthening exercise, but he won’t be allowed to throw for another few weeks at least.
"We have identified why there was a couple of miles per hour drop in his fastball," manager Jim Tracy said. "We are encouraged by this news."
Chacin, who has not pitched for Colorado since May 1, is 0-3 with a 7.30 ERA this season.