The D-backs right-hander experienced tightness in his right shoulder playing catch before a scheduled bullpen session on Friday and has been shut down for three weeks.
Webb was examined by the team's doctor, Michael Lee, on Friday afternoon. It was determined that Webb will take one week off, followed by two weeks of shoulder strengthening, D-backs manager Bob Mevin said after Friday's 5-1 loss to the Giants at Chase Field. Webb was placed on the disabled list on April 13, retroactive to April 7, with shoulder stiffness after making his lone 2009 start on Opening Day.
"Hopefully, this will take care of it," Melvin said. "I think they've done all [the tests] you can do. Maybe they come up with something in the meantime, but that's all I know as of right now."
On Tuesday, Webb threw 33 pitches during a bullpen session, the first time he has taken the mound since being placed on the DL. On Opening Day, Webb allowed six runs on six hits in four innings against Colorado. An MRI performed on April 10 showed no unusual structural damage.
"We didn't expect this, and obviously, after his last bullpen [session], he felt good, and everything would suggest that he was progressing along," Melvin said. "He came out and played catch today and felt some tightness. He's a guy we are going to be careful with. We are not going to push him and see if he can throw through it. He's too important for us to try to push through something like that."
Right-hander Yusmeiro Petit, who is 0-1 with 6.00 ERA in three appearances, including two starts, will stay in Webb's place in the rotation.
Jesse Sanchez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.