The team elected to put him on the DL, retroactive to April 7, after he still felt some soreness in his shoulder while playing catch Sunday morning.
"I want to make sure we're 100 percent when I go back out there," Webb said.
The right-hander began feeling some stiffness following his final start of the spring. He was roughed up a bit on Opening Day, as he allowed six runs in four innings to the Rockies.
Webb was scratched from his next start, which would have been Saturday against the Dodgers, and a precautionary MRI showed no structural damage. The diagnosis from team physician Michael Lee was that Webb was suffering from bursitis, and some fluid in the shoulder might not be allowing for full range of motion.
"It feels better than it did," Webb said. "If there is no structural damage there's nothing to worry about."
Because the stint is retroactive, it's possible that Webb would miss only one more start. D-backs manager Bob Melvin said it was not yet determined who would take Webb's place in the rotation or fill his spot on the roster.
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.