Manager Bob Melvin says Yusmeiro Petit will take Webb's scheduled start Saturday night at home against the Los Angeles Dodgers. Webb will not throw at all for two days.

"For a guy like him, this isn't something you can mess around with," Melvin said before the Diamondbacks played Colorado on Wednesday. "I'd hate for him this early in the season to go out there and pitch with some soreness already, or some stiffness."

Webb, whose 22 victories led by National League last season, experienced stiffness in his shoulder during Arizona's 9-8 opening day victory over the Rockies.

The 2006 NL Cy Young winner blamed problems with his arm angle, resulting in a diminished sinking fastball, for his poor outing. The right-hander allowed six runs on six hits, including two homers, in four innings.

Melvin says Wednesday that "this isn't something you can mess around with" and they will "try to be proactive on this one."

Information from The Associated Press was used in this report.