"Obviously, right now, he's not going to start Tuesday, so basically what we're doing is going as tolerated with throwing," said Red Sox manager John Farrell. "It's likely that at some point we're probably going to have to get him out on a rehab assignment, at least one start for now, but there's no time frame for that. We've got to get him on the mound first and build from there."
Buchholz, who is 9-0 with a 1.71 ERA in 12 starts, is frustrated by the way things are going.
The right-hander injured his right AC joint due to an awkward sleeping position after his start on May 22. Buchholz returned to face the Yankees in a rain-shortened shutout on June 2 and beat the Angels on June 9, but had to leave that start when he developed discomfort in his neck.
"I felt better [throwing on Saturday], but not quite to the point of getting off a mound right now," Buchholz said. "I'm still trying to feel it out. It's taking a lot longer than I want it to. I'm definitely making progress in the right direction. The intensity went up today without any more soreness than yesterday or the day before. Like I said, I'm moving forward -- just not on as quick a pace as I'd like."
There is improvement, but it's more gradual than Buchholz would prefer.
"It's getting better every time I go out," Buchholz said. "There's always one certain spot during the day, when I make a throw or try to put a little more effort into it, it's not a sharp pain but it's definitely something that I feel. If I was to throw 100 percent, it would be a little more intense. I want to be 100 percent off the mound before I get into a game."
Allen Webster was called up from Triple-A to fill in for Buchholz on Saturday night against the Tigers. Alfredo Aceves has been effective three times as a spot starter in recent weeks.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.