Instead of pitching Thursday against the Phillies, lefty Jon Lester will open the three-game series against the Yankees on Friday instead of Buchholz. Franklin Morales, who was activated from the disabled list on Tuesday, will start Thursday's game in Philadelphia.
"Clay went and threw a bullpen today," said Red Sox manager John Farrell. "He feels improved. He still feels some symptoms in that AC joint. When he mentioned that, this is something I took out of his hands. I made the decision to give him another couple of days. He's still a possibility in the New York series, but while he's feeling improved, we felt like it would be best to give him a couple more days as well."
Buchholz still thinks it's realistic he can pitch in New York.
"I want to pitch Friday, but they're going to give it a little more time to feel 100 percent like I have all year and get this moved out of the way, so it doesn't affect me down the road," said Buchholz.
Though the Red Sox don't expect their ace to be out much longer, they'll take a wait-and-see approach.
"I don't know that we have any template to say how fast this would recover, but he indicated that there was still some improvement today over the other day," Farrell said. "Yet the fact that he still feels a little something in there, that's where I was like, 'I'm going to take it out of his hands' and make the decision to give him a couple more days to hopefully get past anything that he's feeling so when he does walk out to the mound there's nothing subconscious in his mind, nothing that he feels.
"The encouraging thing through this is that while he's throwing his bullpens, his arm slot is the same, his delivery's the same. This is located in the AC joint. There's nothing in the rotator cuff. All strength tends are very strong. They're good. They're consistent with Spring Training. This is just something we want to quiet down completely before we run him out there."
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.