Head athletic trainer Keith Dugger wants Butler to go on a rehab assignment before returning. Part of the reason, Dugger said, is that the Rockies want to be careful as they learn more about Butler and Butler learns more about himself.
Butler made his debut a little less than two calendar years after he was drafted 46th overall, as a supplemental first-round choice. The Rockies summoned him from Double-A Tulsa when injuries affected their rotation.
Dugger has not yet heard the results of an MRI performed on Tuesday on Tulsa right-hander Daniel Winkler, who is 5-2 with a 1.41 ERA in 12 starts and has been considered for a promotion to the Majors.
Winkler was a 20th-round pick in the 2011 but gained notice last season, when he led all of Minor League baseball in strikeouts, with 175, in 157 innings at two Class A levels.
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.