It's been a slow recovery process for Webb, who underwent a debridement procedure last August.
Webb threw three bullpen sessions prior to the beginning of Spring Training and seemed to be making progress until early March when he hit a plateau. Since that time, he has played catch and long-toss, but has not thrown a bullpen session.
"I'm just not where I think I need to be," Webb told MLB.com. "But [Lee] reassured me as [surgeon Keith] Meister and [team trainer Ken Crenshaw] that this stuff just takes time and not to push myself too hard."
Webb initially hoped to start the season on time, but when that did not look possible, he had set a target for the end of April. Now with Opening Day just a few days away, late April is looking unrealistic.
By comparison, Major League pitchers Jeff Francis and Erik Bedard have been able to get on the mound quicker. Francis pitched in some Instructional League games last fall after having the surgery seven months prior while Bedard was pitching in the big leagues just under seven months after his procedure in 2008.
All of this has taken a toll on Webb.
"Taking it slow is hard to do when I want to be out there," he said.
Webb was the D-backs' Opening Day starter in 2009, but lasted just four innings before being removed. It was the only time he would pitch all season.
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.