Webb was to throw 60-70 pitches in his fourth bullpen session. He warmed up in the outfield but was scratched after he told pitching coach Mike Maddux that he was still tight.
"It's tough," Webb told TexasRangers.com. "It's really frustrating for me when I'm going good and one day it's like it's pretty good, and then you have a day like this. It's a little depressing. Hopefully we'll push through it and get back on the mound again in three or four more days."
Webb was to toss batting practice Monday, but that was delayed due to weather. Webb said he had trouble getting loose that day as well.
Webb said he didn't feel any pain in his surgically repaired right shoulder but could feel discomfort at the top of the joint.
"I've got a little thing on top," Webb said, pointing to his right shoulder. "I don't know what it is. It doesn't feel anything like what it was. That's good. Concern-wise, I don't know. I'm almost over it. It is what it is. I will go day-to-day a little bit and see where we're at."
Webb has not pitched in the majors since opening day in 2009 with the Arizona Diamondbacks.
Webb will remain on a long-toss program for the time being.
The Rangers signed the 2006 National League Cy Young Award winner to a one-year contract this offseason.