Williams will be available for the game Monday night against the St. Louis Cardinals.
McKenry is hitting .298 in 16 games with the Rockies this season. He has four RBIs and scored six runs.
Williams has yet to play in the majors. He saw action in 41 games for the Sky Sox, hitting .262 with nine doubles and two homers. The 28-year-old was a first-round pick of the San Francisco Giants in 2007.