In four starts, Chacin is 3-0 with a 1.46 ERA, with 16 strikeouts against six walks.
"Right now, I think he's the best starter in the National League, and we need him back," Rockies catcher Wilin Rosario said. "I ask him every day how he's feeling, because we want that guy on the mound."
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. This story was not subject to the approval of Major League Baseball or its clubs.