Chacin, 21, was informed of the decision on Wednesday night, when he was pulled after one inning of a start against Springfield. An opening arose at the Major League level when right-hander Manuel Corpas announced Wednesday that he will undergo surgery to remove bone chips from his throwing elbow.
This season, Chacin is 8-6 with a 3.14 ERA in 18 starts, with 86 strikeouts against 35 walks. In July, he is 1-0 with a 1.84 ERA in three starts, which includes the abbreviated start on Wednesday.
"He's has a tremendous upside," Rockies general manager Dan O'Dowd said. "We're not going to throw him immediately in a back-end role. We'll use him in more of a middle capacity. We'll see how he handles it. This is not an irreversible decision."
The Rockies also are believed to be close to a trade for more bullpen help.
Chacin, O'Dowd said, "took a big step" by pitching a solid inning in the XM All-Star Futures Game in St. Louis during All-Star weekend. The decision was made on the recommendation of assistant general manager Bill Geivett, player development director Marc Gustafson, and Minor League pitching coaches Bryan Harvey and Bo McLaughlin.
"We just feel he's more mature and more focused than some of the other guys we have," O'Dowd said
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.