BOSTON — Right-hander Clay Buchholz, who no-hit the Orioles on Sept. 1 in his second big-league start, is being shut down for the season by the Red Sox.

Manager Terry Francona said yesterday that Buchholz’s strength and mobility, among other things the organization tests for on a regular basis, are not at the levels the Sox would like to see. So rather than risk his promising career by using him over the final three regular-season games and then in the postseason, the organization has decided to err on the side of caution.

Buchholz called himself “sort of bitter” about the decision.

“I feel a little bit tired right now, but it really wasn’t a big deal to me,” said Buchholz. “When they called me into the office, I knew what it was about. They said they’ve been thinking about it for awhile; they’re thinking about the long-term issue.

“I understand that . . . but it feels like, all the hard work and the year I’ve put together this year, and to go home, I’m sort of bitter about it. It makes me want to work even harder and get back here next year.”

Francona met with general manager Theo Epstein and others in the organization to discuss Buchholz’s status. Buchholz, who turned 23 last month, was told yesterday.

“Obviously this wasn’t our first choice,” said Epstein. “It wasn’t even our second choice. It was pretty much our last choice. Unfortunately, this is something, after talking with the medical staff, we have to do. Clay has been suffering from fatigue and a weak shoulder — on and off — this month. It’s to a point where he can’t pitch safely in October.”

Francona agreed.

“We test all of our pitchers and Clay is at the point where we’re not real comfortable about having him go out there and pitch. He quite possibly could do it, but with what the future holds for him, we don’t think that’s the right thing to do,” said Francona.

“There’s some fatigue, and with that comes a lacking of strength,” added Francona. “To pitch him now, it would be very disrespectful to try and get some innings out of him. That’s something that would not be in his best interests.”

There had been much talk this month, especially after his no-hitter, that the Red Sox were placing a ceiling on his total numbers of innings pitched this year in an attempt to keep him healthy for the future. Francona indicated yesterday that the ceiling hadn’t been reached, that this decision was strictly because his arm was showing signs of fatigue. Not injury, stressed Francona, but fatigue.

Buchholz, who began the year in Double-A Portland, moved up to Pawtucket in July before a quick trip to Boston for an Aug. 17 start. He was sent back to Pawtucket after that game, an 8-4 win over the Angels, but was called back up on Sept. 1 when rosters were expanded.

Buchholz pitched only twice after his 115-pitch no-no. He worked three innings in relief in Baltimore on Sept. 6 and he started against Toronto on Sept. 19, working the first 4 2/3 innings, throwing a total of 68 pitches. He took the loss in that one, a 6-1 setback. Buchholz, who showed impressive command with his fastball, curveball and changeup, finishes his first taste of the big leagues with a 3-1 record and a 1.59 earned-run average.

Before making it to the big leagues Buchholz went 7-2 with a 1.77 ERA in 16 games for Portland and 1-3 with a 3.96 ERA in eight starts for Pawtucket.

Buchholz had thrown some side sessions in the Boston bullpen this month, but Francona said the Sox kept him from throwing for four or five days so they could get the most accurate possible readings of the tests. The Sox, he added, were “excited” about the prospect of Buchholz contributing in the postseason, but had to be objective when it came to looking at the test results.

“He’s been shut down for the year and he’ll start his rest for the offseason,” said Epstein. “He needs to go have a great winter of strengthening and conditioning and come back ready to throw a lot of innings next year.”

jmcdonal@projo.com