Webb said after his club prevailed, 9-8, in the season opener against the Rockies on Monday that he experienced some stiffness in the shoulder late in his four-inning outing. He subsequently played catch before Tuesday night's game and told reporters he felt fine, but that evidently wasn't the case when he arrived at the ballpark on Wednesday.
"Hopefully it's just some lingering soreness, and our training staff will work diligently on that the next few days," Melvin said. "Hopefully that's all it is."
Melvin added that it was too early to worry about sending Webb out for tests.
"I don't know," the manager said. "We haven't gotten to that point yet. We'll wait and see how he feels [Thursday]. The doctor will look at him again today."
The stiffness limited Webb's effectiveness on Monday in the fourth inning, which began with Troy Tulowitzki and Chris Iannetta hitting back-to-back homers on his first three pitches. An inning earlier, Webb walked the bases loaded with two outs and allowed Brad Hawpe's bases-clearing double. Webb was lifted by Melvin after the fourth.
Webb wasn't available to speak to the media on Wednesday. The Diamondbacks have an off-day on Thursday, and they open a three-game series against the National League West-rival Dodgers on Friday night. The club said Webb will be available to the media before that game.
Webb, who went 22-7 with a 3.30 ERA last season, was the runner-up to Giants right-hander Tim Lincecum in the voting for the National League Cy Young Award, an honor Webb captured in 2006.
Webb said he battled through an early bout with right shoulder tendinitis last season, and he needed four starts from Aug. 26 to Sept. 12 to notch his 20th victory.
This spring, Webb had a start pushed back because of tightness in his right forearm. And Melvin revealed on Wednesday that Webb also experienced some shoulder stiffness during the course of the Cactus League season.
"I think there was a day when he had a little stiffness during Spring Training," Melvin said. "[The forearm] was a little different. This was in the back of the shoulder."
Webb, 29 and a veteran of five big league seasons, noted that the shoulder stiffness on Monday contributed to a marked decrease in his velocity, as he tried to find the right slot to rotate his arm as he followed through on his delivery. Webb is most effective when he's able to come right over the top, allowing his trademark sinker to drop. His sinker flattens out as his arm motion dips even slightly to the side.
It all sounds eerily familiar to the problems he noted during his slump last year.
"I mean, it's similar," Webb said on Monday. "Pitchers go through times when you try to find the right spot and you try different things. You just have to kind of work through it until one day you find it, it clicks and you're able to repeat it."
Last season, Webb exploded out of the gate, opening 10-0 in his first 10 starts, including six innings of two-run, three-hit ball in a victory over the Reds at Cincinnati on Opening Day.
Obviously, Melvin said, Webb's problem is certainly a concern, coming this early in the season.
"I'm concerned enough that he's going to skip a start," Melvin said. "With a guy like him, this isn't something you can mess around with. It's too early in the season for him to go out there and pitch with some soreness already.
"He played catch [Tuesday], and it was OK. Then he came in today and it was bothering him a little bit. I'm going to try to be proactive on this one."