Bettis allowed 13 earned runs over 13 1/3 innings in previous stints with the Rockies this season.
"I think we're bringing him back at a good time," said Weiss. "He went down there and worked on a few things. Mentally, he feels real good where he's at."
• The Rockies designated right-hander Wilton Lopez for assignment on Monday to make room on the 40-man roster for right-hander Christian Bergman, who was promoted from Colorado Springs to make his Major League debut.
Lopez allowed eight earned runs and 18 hits over 6 1/3 innings before the Rockies optioned him to Triple-A on April 9. He didn't fare much better following his demotion, allowing 39 hits and 15 runs over 29 innings with the Sky Sox.
"Wilton could still end up with us; you've got to go throw the process," said Weiss. "We needed to create a spot; unfortunately, Wilton was the guy we needed to create a spot with."