Oswalt battled through back pain in his final four starts of the year, including Tuesday against the Reds when he gave up six hits and four runs in six innings. Astros general manager Ed Wade announced the decision after consulting with Oswalt, manager Cecil Cooper and head athletic trainer Nate Lucero.
"It's not getting any better and [it's] kind of lingering a little bit," Oswalt said. "If we were in contention and fighting for the playoffs, I would try to get an epidural block and ride it as long as I could. But I don't want it to linger for next year.
"We decided it would be best. If I skipped a start, I'd be looking at two starts [remaining] and not being able to throw in between starts. It doesn't make a lot of sense to try to throw two starts, especially with young guys up here, and you'll be able to see young guys go in my spot."
Oswalt, 32, went 8-6 with a 4.12 ERA in 30 starts this year, setting a club record with 16 no-decisions. Eight wins are the lowest total in his career, and he will go into next year tied for second place on the club's all-time wins list at 137 with Larry Dierker.
Oswalt has been dealing with a bulging disk in his back since 2007. Last year, he had a pain-killing injection in the sciatic nerve in his lower back, which had become inflamed and was causing the pain in his left hip and left leg. Wade said the condition can't be corrected with surgery, and Oswalt has already begun a swimming regimen to help build core strength.
The back has bothered Oswalt since his Aug. 31 start against Chicago, and he left his start against the Braves on Thursday with back tightness. The back flared up again in the fifth inning of Tuesday's loss to the Reds and was forcing him to make a change in his mechanics.
"When I got here this afternoon and talked to Coop and Nate Lucero and we met with Roy, and he indicated that with the issues that he's been having with his hip, he has different types of soreness in his arm, which would indicate he's probably changing his pitching mechanics," Wade said. "We just can't let that occur. It doesn't make any sense for us to continue to ask him to go out there with the hip issue knowing it could lead to an arm issue.
"We talked about staying on course to make his next start or skipping a start or shutting it down altogether. Making his next start on time immediately came off the board. So then it came down to whether skipping a start made sense. If he still had a start on the near horizon, he'd still be trying to throw bullpens and play catch and things like that, which would potentially exacerbate the problem. Rather than leave that temptation out there, we decided to go ahead and shut him down."
Oswalt will be examined by team doctors when the club returns to Houston on Monday. Wade didn't know who would take Oswalt's place in the rotation, but with an off-day on Thursday, the Astros wouldn't need an extra starter until next week.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.