Feltner was optioned to Triple-A Albuquerque on Saturday.
Feltner was called up to make his major-league debut Sept. 5. He struggled in two starts with the Rockies, allowing eight earned runs across 6.1 innings. Jon Gray will move up in the rotation and start Sunday in Feltner's place, and Feltner's absence could allow Peter Lambert (elbow) to work as a starter to close the campaign.