The team will make an announcement regarding Buchholz on Tuesday, manager Terry Francona said following Monday night's game.
"We'll have the whole thing tomorrow," Francona said. "We'll let (team physician) Dr. Gill draft a statement and explain it, and then I'll answer anything you guys want, but it'll be easy tomorrow and a little more informative."
The right-hander was moved from the 15-day to the 60-day disabled list Sunday to make room for new acquisition Erik Bedard, and he saw a back specialist Monday in Los Angeles. If the move to the 60-day DL is dated from when he went on the DL June 19, he will have to miss at least a few more weeks.
Buchholz has been suffering from what the team called a lower back strain.
The fracture was first reported by Comcast Sports New England.
Red Sox manager Terry Francona did not have new information on Buchholz's condition late Monday afternoon.
"The update we have is Clay was seen by Dr. (Robert) Watkins and the appointment's done," he said. "We need Dr. Watkins, Tom Gill, Mike Reinold and all the medical people, Buch and Theo (Epstein) to have a chance to sit and meet and talk and kind of sift through things."
The stress fracture was discovered during an MRI last week, according to the report. Buchholz had felt normal soreness immediately after a bullpen session July 25, but the next day he felt additional discomfort. Buchholz's next throwing session, which was to have been last Wednesday, was canceled, and an appointment was made for the pitcher to see Watkins.
Sunday night, Epstein hinted that the club did not expect good news after Buchholz visits Watkins on Monday.
"Clearly, we have some concern for Clay," he said. "It's been a couple of months now, which is longer than we expected it to be. We're still awaiting some more feedback and another opinion. I think we have a feel for what might be going on, but Clay is seeing another expert (Watkins) to get his opinion and then we're all going to put our heads together this week.
"I'll refrain from answering in too much detail until we have a chance to talk to Clay and we have a chance to talk things through. ... We think we're in the process of getting to the bottom of it, and we're all going to put our heads together early this week and talk about it with Clay before we discuss it publicly."
The club did not reveal that Buchholz had an MRI last week, even though it often does release such information, and as recently as last Friday, Francona was referring to the injury as a "muscle strain." Asked last Thursday if the club was concerned that Buchholz would not be able to pitch for the rest of the season, Francona said: "Not right now. It's not the simplest muscle strain we've ever seen."
Minutes before the trade deadline Sunday, Epstein traded with Seattle for the left-handed Bedard, indicating that the Red Sox needed an insurance policy at best, or at worst a replacement for Buchholz.
Mets third baseman David Wright recently returned to action after missing two months with a stress fracture of the back.
Buchholz is 6-3 this season with a 3.48 ERA. He was coming off a stellar 2010 season in which he went 17-7 and was second in the American League with a 2.33 ERA.
Joe McDonald covers the Red Sox for ESPNBoston.com. Gordon Edes of ESPNBoston.com contributed to the report.