"Clay Buchholz has esophagitis, which led to an erosion of the esophagus and an associated gastrointestinal bleed," the club said in a statement. "He has been evaluated and observed at Mass General Hospital. Clay is doing well and is expected to make a full recovery."
A Red Sox source who talked with Buchholz did not expect the absence to be months-long and said the right-hander was eager to get out of the hospital.
Buchholz went to the 15-day disabled list on Sunday. Whether he'd need more time than away was "something we're dealing with every day," manager Bobby Valentine said.
"Clay is stable," Valentine said. "I think that's good news."
Buchholz is 8-2 with a 5.53 ERA in 14 starts this season. He has not pitched since June 19 vs. the Marlins. In four starts this month before going on the DL, Buchholz was 4-0 with a 2.40 ERA and 25 strikeouts in 30 innings.
Aaron Cook assumed Buchholz's spot in the rotation on Sunday, making his second start with the Red Sox. Cook allowed three runs in five innings to beat the Braves.
According to the U.S. National Library of Medicine's website, "Esophagitis is a general term for any inflammation, irritation, or swelling of the esophagus, the tube that leads from the back of the mouth to the stomach."